I would personally get the one-size diapers because they grow with your baby. We currently have 12 BG3.0s that we use at day care and we use Flip covers either with their inserts or a prefold at home.
If you start off with this, you'll get an idea of what you like. The AIO's are nice for quick and easy changes. It really depends on how often you want to wash diapers, but most recommend every other day.
Re: Question for CDers
That's really great! Thank you
I recommend this website.
ETA: You need to use the drop down menu to choose 'How many diapers do I need'. I guess I can't link directly to that.
After tons of research and talking to a lot of CDers at Diaperswappers.com and a local mom's group I'm in, I came up with:
6-8 covers
12 newborn prefolds
12 fitteds
4-5 AIO's
If you start off with this, you'll get an idea of what you like. The AIO's are nice for quick and easy changes. It really depends on how often you want to wash diapers, but most recommend every other day.