This post lists the sizes of the different precut fabrics:
http://www.quiltingboard.com/posts/list/25065.page
The quantity of each varies by manufacturer. If you buy on eBay, pay attention to the quantity...they vary greatly as some are probably cut by the sellers rather than the manufacturer. The most consistent quantity wise is probably Moda.
I've just started buying precuts. It probably costs more upfront, but you can get a wider variety of prints cheaper that way than buying 1/4 yd of each different print in the pack.
From what I've read here, the majority of people do not prewash their precuts. I didn't, even though I prefer to prewash my fabric.
You can check out books at the library or free patterns thru the fabric manufacturers websites.