FYI:

If texturing for renders (not games) you don't have to try to fit an entire mesh's UVs onto one texture or anything. You can have a texture for the face, a texture for the eyes, a texture for the hands, etc if you wanted.

If texturing for game type stuff, that's when you want to try to fit as much as you can onto a single texture map. Typical game texture resolutions are:

1024x1024
512x512
256x256
128x128
etc.

Normal maps, spec maps, etc are all free to use. Feel free to zbrush the heck out of these things if you'd like.