1. I haven't used it, but I've heard very good things about Reaper. It's free, so you might as well give it a try if you're interested.
2. It all depends on your ram allocation. Most people use wavs only for music and dialogue and mp3's of some other supported lossy format for everything else.
3. The largest sound files are usually atmos, music and dialogue; shortest, sound effects and wild foley. It all depends, though. Audio for cutscenes tends to have much bigger files, though.
4. Sound on Sound (http://www.soundonsound.com/), Designing Sound (http://designingsound.org/) and Audio Tuts (http://audio.tutsplus.com/) have very good tutorials that cover everything from DAW's and recording techniques to sound design.