How much of the sound quality would you attribute to the microphone itself and how much to elements such as mic placement, room acoustics, musician quality and subsequent editting??
It depends on the mic. If you have a regular dynamic mic, which has a rather limited area from which it takes up sound, the room in itself isn't that important, but like someone said, you might want to place something soft behind the mic to soak up nasty noises and unwanted frequencies and overtones (no no, not Overtons). With a condenser the room is much more important, especially if it isn't hyper cardioid (this means that it has a very limited angle at which it picks up sound, only from the front, straight in, nothing from sides or from behind).
When it comes to musician quality. Well... the better a mic is, the more "honest" it usually sounds, what you play is what you get. No mic in the world can make a poor player sound good, but conversely a poor mic can make a great player sound bad. And "creating" a good sound with subsequent editing should never be the goal. Unless you happen to be a master of physics and acoustics and have some very high end software, you'll never be able to take a very poor recording and with the use of EQ's and effects sculpt that sound to something good. And even if you do, it wouldn't sound very natural.
So basically what I'm trying to say is that what you should be going for is something that'll give you a good, clean recording to work with. Everything else is just the icing on the cake. A saying in the world of studio work is that it is much easier to edit something unwanted out of a mix when it's there, than editing in something that you want, but isn't present in the recording.
With that said. Go nuts. While reading up on mixing and editing and what not can be a great way to learn, there's nothing like mucking about, trying crazy things and going "hey, I wonder what this button does!" Just remember to save whatever you were doing and want to keep.
