If you go to any parenting board you will find LOTS of info. I Would recommend sheknows.com and familygarden.net. They had some pretty strong diapering communities in the past.
I bought my diaper covers from:
http://www.thebabymarketplace.com/
I have not bought any in over a year, but they often had free shipping, great deals, and were fast.
It depends how often you want to do laundry for the most part. At the newborn stage you need 80 per week at least. YEs - 80!!!!!! I personally use a diaper service, so we bought the covers, and the diapers are provided. Initially 80 per week, and whittle it down from there. On average you will need 60/week over the long term. We went down to 40 when my littlest turned 1. IT is not near enough, but we go out of town enough and he can not wear cloth at night - he gets soaked and wakes up for changes so we switched to disposables at night. My first son never cared - he was cloth all the way. SO it will depend on that too. In general I think we bought 8 covers to wash every day or 2. The covers do not have to be changed every time necessarily so we could stretch 8 out for 2 days sometimes. We probably did more laundry as we needed to as a result, I would recoomend more like 12. You will need more diapers than covers probably.
You may want to hold off until the baby arrives. I Would not buy too many newborn sizes or anything, the baby may outgrow them fast, or may not even need them.
We went through the small size in just few weeks, the medium maybe lasted a couple of months, and large has lasted 2 years+. Newborn size was too small for my boys. But get ideas of what you want to buy and maybe wait to buy them until your baby is born. My boys were really on the big side. You could end up with a baby in a size small for a year - I Would not invest too much until you give it a try and make sure it is going to work. & can guage size better.
Definitely check out those boards - they will have far more advice than I. I went with the cheapest diaper covers I Could find - hehe. They have done me well.
Good Luck!