I do home-childcare. When DS#1 was a baby, I did it for just one other child that was a bit older than DS, who was a neighbor. So, I agree that to start out, having just 1 other child is a good idea.
I've gone off and on since then depending on where we lived. Like, for a couple years, we lived WAY out in the country, so I would take DS and drive into the town and be a nanny for another family. That paid great, but it was hard trying to raise my own in some else's house all day, KWIM? I was glad when I got pregnant with #2 and had the excuse to quit.
Now, I live right in the city, my kids are 4 and 7, so good ages to adjust to lots of other kids being here all day. I watch 5 kids, only part-time, so only 2 extras per day (these are per rules of the state to stay un-liscenced, and rules of myself to keep my sanity!). I have learned through experience, that I really only like providing part-time care. I try and do 2, or occassionally 3 days per week per family, because otherwise, I get sick of the kids, and I don't want that! That said, I also do drop-in care, so often have 1 extra random kid with us

So, let's see, to answer your questions:
1. I do not have liability insurance, and do not worry about it, but I guess that boils down to your comfort level. Also, if you were running a big scale daycare, of course you'd have to have it, so I don't find it necessary in a small home setting.
1-1/2. I take charges in and out of the car by buckling and unbuckling seatbelts

. I own carseats for all the children. I drive a minivan. I also use the city bus system as much as I can. I know some mom's think I'm crazy to take 4/5 kids on the bus, but I find it much easier than loading/unloading that many kids. Our bus is really only best for going downtown, and our house is a short walk to the bus stop, so that's a good option for us when we do things like story time at the downtown library.
2. Rates are subject to area. Check out the local classified paper you have and see what folks are charging. Realize that the really cheap rates are moms popping kids in front of the TV and feeding them jello and fruit loops. You can also call around and ask providers their rates. Rates also depend on if you provide a curriculum, IMO - how many of your own kids will be there, if you provide food -and if so, what quality of food is it, if you go out in the community to do things (library, field trips, playgrounds), etc.
3. I put all the nappers in my queen size bed that is on the floor. I have to selectively place the children so they won't bother each other (you'll quickly learn which kids fall asleep as soon as they lie down, and which kids need to twiddle their toes for 15 min before they can fall asleep). If for some reason, I have an excess of nappers in a day, I'll pull out the futon in my room, and also use that. I close the blinds, shut the doors, lie down in between kids (this is where the selective placement comes in), and read a story, sing a lullaby or 2, then lie with them until they zonk out.
Most kids who come to us are of similar parenting styles, so would freak out if they were just left alone to fall asleep, but sometimes we'll get a drop-in who's used to a more institutional daycare setting and can swing it.
4. Answer above

Good luck!