We have about 50 and I wash every 2-3 days because I am scared that the ammonia will build up lol. However, DD is 16 mos and I have never had an issue. The washing is really easy and you easily adjust to the new routine.
I purchased the two of the Econobum starter kits, so we have 24 prefolds and 6 diaper covers. I wash them every other day right now for my 2 month old.
Re: How many cloth diapers should I buy?