#2
hendrix used some, my digitech gnx4 has one but i dont know who makes like a solitary harmony pedal.
#4
Do you mean harmonizing as in playing 1st and 3rd notes together as in CE DF EG etc...... then you'll need a Whammy (decent IMO), Boss PS-5 (better), or........... Eventide Harmonizer (dude its 4,5 grand don't, ask someone like Steve Vai on its quality)
Tone is all ...... well probably 75%, in your fingers.
The rest depends on your wallet's thickness !!

Keep the faith, baby!!