I'll give you my take on your questions, too, if you'd like! Be warned, I have too much to say sometimes.
Diapers - I've used both cloth and disposables. I prefer to use cloth because I feel that, overall, it's the better choice for the environment. However, I'm not as "militant" about it as other people can be. We used one pack of newborn disposables with both boys at the start because the meconium poos (first BMs that are very tarry and black) are super messy and can stain. I also thought we should go easy for the first few days, while I'm supposed to stay in bed (midwife's orders). Never regretted that decision. I also used disposables on trips (tried cloth on my first trip "home" to visit family, and it was a big hassle toting around dirty diapers, worrying about the use of fabric softeners in other people's machines, etc., so we just never bothered after that), and I find I need to switch to disposables after about age two-and-a-half. I found by that point, with both of my boys, their urine was just too stinky or maybe it's their poops, but man! I can't get the diapers to stay clean smelling after that point. As for their ease of use, I'd say they're not as bad as most people think. While the baby is exclusively breastfed, you can just put dirty ones (poo and pee) in your diaper pail and then do a rinse cycle before you wash. After they start solids (or if they're formula-fed), you just dump the solids into your toilet (which you're supposed to do with disposables anyway), and then you can rinse them. Some people swish them in the toilet. You can also get a diaper sprayer that attaches to your toilet that is basically a hose to rinse them. We've always rinsed ours in our laundry tub, and then wrung them and left them hanging on the edge, along with the rinsed poopy wipes, until wash day. A rinse/quick wash cycle, and then your wash routine. The washing routine is the trickiest part about using cloth diapers, but it's really not so bad once you find what works best for you. The rules of thumb are to use as much HOT water and as LITTLE detergent as you can get away with. Also NO fabric softener at all (and don't use it in your machines for any other load either; it leaves a build-up on your diapers that diminshes absorbancy and adds to stink problems, too). It's best to use an approved diaper-friendly detergent, but most "free and clear" detergents will do as long as you use way less than for a normal load. And then RINSE until no bubbles are visible in an agitating machine (I found jsut doing one extra rinse was enough). There are some great resources out there to determine which detergents are good or bad for diapers. You can also get all that information, and buy the best products, wherever you'd buy cloth diapers. (Whew! Sorry for the book! I researched A LOT before my first was born, and then had about five years of experience using cloth diapers. I know too much! :P)
Baby Powder - I still have the (full) bottle I got as a shower gift for #1. Not necessary at all, and really, not that healthy either. Talc is bad, but any kind of powder is a breathing hazard. Best to avoid it, in my opinion. If you're concerned about rashes, the best thing to do is use as perfume- and chemical-free products as you can, and keep baby as dry as you can. If you use cloth diapers, you WILL be changing them more frequently. (I don't care what the cloth gurus say! It's true. They can go much longer, especially when they're older and not pooping all the time, in a disposable diaper.) If rashes are a problem, there are plenty of great ointments and creams out there. Be aware that anything with fish oils (Desitin) or zinc-based (Zincofax, Sudocreme, and the like) are not cloth diaper friendly, if you're using cloth. You can use disposable liners in cloth diapers to use these products, or find a CD (cloth diaper) friendly product (there are lots, especially at the stores that sell CD's).
Onesies - And colored clothing in general. I'm not one to be paranoid about dyes and fabrics, so my kids have worn whatever is available in major retail stores. However, I try to avoid scratchy tags, tight necklines, and anything that has too many snaps/buttons/etc. Many people like to avoid the kind of onesies that have to go over the head and opt for ones with snaps all down the front because of frequent diaper blowouts and such. I found that using cloth diapers made poop blowouts virtually non-existent (there's a great reason to use cloth!), so it wasn't really an issue for me. But make sure they can slip easily over the head. Nothing worse then trying to wrestle a piece of clothing off a screaming baby in the middle of the night!
Sling - I knew nothing about babywearing with my first. I wish I had taken more time (any time!) to look into it, because I loved it later on. I used a wrap-style sling (like a Moby) for my second right from the start. They are so great for that newborn stage! After they get to be about twenty or so pounds and have good head control, I like to move over to a soft-structured carrier (like an Ergo). Other people have other preferences. I would definitely suggest trying out different styles of slings AFTER birth to see what works best for you, the baby, and whoever else might be carrying the baby a lot (like dad). You may be surprised what works best for you and what you don't like. Many stores that sell them will let you do this in the store, or even let you take a few types home for a trial. But, in general, you probably won't go wrong getting a wrap before the baby is born. I think pretty much everybody likes them, and they're a relatively inexpensive choice in comparison.
Strollers - Some people are very anti-stroller, but I made great use of mine. Especially my double jogger after I had two! I don't drive, so this was my way of getting out with the kids easily, and it was good exercise. I don't like to put a baby in one (aside from in an infant bucket seat that can attach to it) until they are several months old and can sit well in it. Depending on how much you will use it, and where, you may find different types preferable. If you plan to use it a lot, on all types of terrain and in all types of weather, I highly recommend a jogging style one. That is, one with three (or sometimes four), LARGE, rubber, air-filled tires. They can just go so many more places! It doesn't matter if you don't jog. If you plan to use it mostly in malls or other indoor areas, a regular stroller will do. If you don't think you'll need one very often, or if portability and/or cost are issues, you can consider a folding, umbrella style. These are the most bare-bones, and least comfortable for you and child, so I would only recommend that type if you're on a very tight budget, will only use it very infrequently, or will almost always be traveling on a bus and need it to take up little space. Otherwise, I recommend getting the best you can within budget. Most people I know usually regret not getting the better one they could have once they're really using theirs and find problems! Think hard about features you really want or need, and then go from there.
Car Seat - Definitely a necessity! As LivingSky mentioned, you can start out with a bucket seat (the typical newborn seat that can be detached from the base and carried around by a handle), or go right into a quality convertible seat. It depends on your needs. What I liked about using a bucket seat was that I could bundle up my baby (with a cover that goes OVER the top, never under the straps!) inside the house in the winter and carry them out to the car warm. But I almost always took them right out and into the wrap or my arms after we got to the store, or whatever. I don't like to see babies hanging out in them all the time, either! The biggest thing about car seats is to get the one that installs best in your car. That will be your safest choice. Do some research. Try to install different seats in your vehicle (Babies 'R Us will let you take them out to the car). I highly recommend checking out car-seat.org for more information about what seats are the best in your particular vehicle, and tips for proper installation, and proper placement of straps and clips and such. Or better yet, consult with a live car seat technician! (Don't take advice from Babies 'R Us or other retail employees. Some might know what they're talking about, but there's no guarantee.) Also, please keep you baby rear-facing as long as possible (within the safety limits of your seat). It really is so much safer. (Just my personal plea. It's a pet issue of mine.)
Breast Pump - I tried it both times. I really did. I just did not produce any extra milk. Thankfully, it was never a necessity for me to pump, as I'm a stay-at-home-mom. In your case, going back to work and being sure you want to pump, I would consider looking into renting (or buying, if you can afford it), a good-quality, electric, double breast pump. They're much more efficient and will save on frustrations later on. If that's not feasible for whatever reason, there are good battery or manual ones out there. Check reviews and prices.
Changing Table - I'm a big-time changing table user! Mine's been in constant use for almost six years now! (Yes, yes, I know. I need to get my three-year-old potty-trained! :P) Even using disposable diapers, I always use a basin of warm water, soap, and wash cloths to change my kids. That's just so much easier to deal with in a specific location and with them on a table. However, when we're on the road and use disposables and disposable wipes, it's very easy to change them pretty much anywhere, so let your choice of diaper and wipe system help determine your need for one.
Pacifiers - There are many different opinions on these! I'm in the camp of not minding it when they're little (under a year), but preferably not after the first few months. I think they are a great soothing tool for the wee little ones. Sucking is just such a natural urge for them, and having that option gives mommy's boobs a break. ;) Unfortunately, neither of mine wanted anything to do with them (except my first would take it in the car for a little while), so *I* was the human pacifier. That has definite downsides, believe you me! Especially if you plan to go back to work. My opinion is, don't start it right away, but if you feel the baby might "need" it after a while, you can try one and see if it helps. I don't really think there's much to worry about regarding tooth development unless they're still using one at, say, age three or four or something. But, again, some people have stronger feelings on that. :)
Where to Buy - Most of the above things, you'll be able to buy used to save money. DEFINITELY always buy a new car seat, though. You just never know if a used one was in an accident or not and is safe. Babies 'R us, although I've mentioned it a few times, is one of the more expensive places ot buy things. Check around for sales. Get what you can before the baby is born, as sales come up. Cloth diapers and slings should come from a natural baby store that specializes in them. Please don't buy Kushie brand cloth diapers or Snugli slings to save money! They are inferior products and will make you hate babywearing and cloth diapering. Go for the quality stuff. You can get those used, too, once you know the brands you like. Check on kijiji, at thrift/consignment stores, and at baby thrift sales. Natural baby stores will often host used item sales occasionally as well, so that might be another option.
Okay, well I warned you! LOL! But I hope some of that was helpful.