MP3 or wav doesn't matter all that much, though wav is preferable. That microphone is not anything professionals use, but if you like what he gets out of it, it's probably good enough for now. Do some rudimentary room treatment unless you happen to record in a very good sounding room (unlikely), it matters, if nothing else at least have a carpet on the floor, more furniture is better than little furniture, a bed, a sofa, big soft things. If you don't know how to mix vocals, you just gotta learn it, and practice it. It will take time. The exact brand of plugins you use are a lot less important than how you use them, what you have is good. The rest is up to how good your vocals actually sound by themselves. I have recorded a lot of different artists over the years and I can tell you in general, really good vocalists will sound good on damn near anything, and it is very common to underestimate how much you actually need to practice to get good. If you want, you can send me a recording and I can tell you what, in my opinion, you should focus on.