Re: Compressor
I don't think you need to spend a fortune on a good compressor. I don't think you can go wrong with the ubiquitous Boss CS-3. You can find them used for 50-60 bucks. Tried and true. The MXR Super Comp has a good rep too. The standard Dyna-Comp might not be suitable for metal...it has a particular sound.
Compression can give you a more polished sound, evening out the sound. I find it helpful when I want to add a little fullness at low volume; to add sustain to lead lines, to help tame a powerful amp and reduce dynamics, to make funk rhythms pop, and it's mandatory for chicken pickin' and very handy for the acoustic guitarist that both flat-picks hard strums and fingerpicks as well.
I'm usually using just a small amount of compression. Usually I set the amount of compression to where I can just begin to hear it "pump" and then I back it off slightly.
I hope this helps.
Bill