I'll give my opinion as well.
As far as when to get things. I'd wait until you are out of the first trimester. Which you probably are by now?
Then you don't really need to buy anything until the third trimester unless you get really good deals. If you see a pack and play or one of those bed side co-sleepers you really want on craigslist or on a major deal somewhere, then you can think to get it if you have the funds handy. I'm kind of an in between person on this place. A little "crunchy" a little not when it comes to baby care.
I would want a nice baby carrier. I could never figure out a sling, so be aware that could be a challenge. I prefer soft formed carriers. I really think the beco looks great for newborn and up most likely. I have an ergo and a boba, but they only worked if I had baby swaddled and then put her in the carrier. You want one that allows skin to skin contact if you are going to breastfeed. Breastfeeding in a carrier is super convenient, especially when you are out.
I liked the my brest friend breastfeeding pillow. I could never make a boppy work because I have a long torso and I'm tall. You have to buy that one a little in advance to let it off-gas. I personally couldn't make anything else work (except a carrier) as well for support while breastfeeding, but to each their own here.
Get a good breast salve or cream for your nipples. http://inhishands.com/New-Mother-s-Healing-Salve.93 - my personal fave.
I'd want a pack n play with bassinet feature for newborn. I cannot sleep with my baby. It just never worked. I'm a light sleeper and deathly afraid of waking the baby up when it isn't time. LOL
A car seat is essential. I like bucket seats, the ones that pop in and out for the newbie stage, but start to not like them with an older baby. But, you can always just not pop out the seat once they are beyond that.
If you are going to breastfeed. I recommend cloth breastfeeding pads. The disposable ones didn't work very well for me. But, maybe you will be different. Just a personal preference. I like the ones with a PUL backing and a microfleece layer next to the skin. I have some like that with hemp as the absorbent layer. I usually had to add an extra doubler pad that was made of thick cotton that I bought off of etsy because I leak like crazy for the first 3 months of breastfeeding. I'd recommend having twice as many changed of those as feeding sessions for a day. I'd say there's typically between 8 and 12 sessions a day for a newbie.
I'd get something to swaddle baby in. I tried not swaddling and it didn't work for me. I definitely recommend swaddling. I'd do it the traditional way as most of the swaddle wrap things don't wrap the arms tight enough to do a good job. I have babies that can escape otherwise and then they wake themselves up every 15 mins. Lovely stuff. haha
Cloth diapers are something you should look into. If you don't like them, that is fine, but at least look into them so you can make an informed decision. http://jilliansdrawers.com/newtocloth
I started with paper diapers and saw a women with cloth diapers and couldn't believe how different they were than what I had imagined. She had some all in ones. It started me on my journey to part time/most of the time cloth diapering.
Then of course you need some clothes. I'd recommend onsies and sleepers. Since it's a summer baby. Get lightweight sleepers, no fleece. If you are having a baby shower, register for some of these things and see if people buy them for you first. Onsies and sleepers can be really cheap when you buy them in the multi packs. The amount you'll need will depend on the baby, but it's nice to have a lot for the first few months because they get soaked in your milk or formula from spit up, or they leak through the diaper and you need a change of clothes. But, you could start with a smaller amount and go buy some more if you think you need it.
I would want a stroller. If you have a good back though, you can just use the baby carrier until they are old enough to hold their neck up and buy a less expensive stroller that way, instead of something that reclines back or pops in the carseat. But, getting one that pops in the carseat can be nice. It'll be up to you for what you prefer.
That's all off the top of my head.