#2
Well, here are the tonalities of each.

Ionian...major
Dorian...minor
Phrygian...minor
Lydian...major
Mixolydian...major
Aeolian...minor
Locrian...diminished, or minor if you remove the flattened 5th (thanks, LogZ )
#4
Yep you'll find that the minor modes tend to have a sadder 'feel' to them but will probably also depend on what key and progression you play them over. The Locrian is more evil sonding though - I think Slayer use it quite often.
#5
Ionian...major - Happy sound
Dorian...minor - Minor sound, but not as dark as natural minor
Phrygian...minor - Spanish feeling, good for metal
Lydian...major - Dreamy feeling
Mixolydian...major - Really happy sounding!
Aeolian...minor - Minor sound
Locrian...diminished - Very dark sound

not great descriptions but the general idea is there