#2
you can. i havnt ever tried it. what amp are you using the distorion pedal on? try it any see if it works. i dont think it will sound good though. when you push an amps dirty channel with a OD your pushing the tubes harder. A distortion pedal clips the signal causing distortion, so i dont think it will sound good to boost a clipped signal.
#3
I used to use an Ibanez TS-9 to boost my Big Muff, I sold them both though and upgraded.
Main Gear:

ESP Eclipse CTM I
Dean 'Shards' Razorback
Chapman Guitars ML-1
Ibanez AEL40SE Acoustic
Blackstar HT-5 Mini Stack
EHX Metal Muff
EHX Small Clone
#4
Of course you can

I use a SD-1 to boost my Tri-AC for solos.

I also run my big muff into the top boost channel of my AC30 to get it nice and gritty. You can use any of combination of OD and distortion and play around til you find something useful. Sometimes the applications have limits, but you'll find a use for it somewhere

Edit: forgot I also run my Tri-Ac into my top boost channel to add a nice growl to the sound, sounds great!
Ibanez SAS32FM
Dunlop Crybaby
Korg Pitchblack
Boss LS-2
Boss SD-1 + 2 x Clones... all modded of course
Fulltone GT2
Hardwire DL-8
Big Muff (Russian)
Vox Pathfinder 15R
Vox AC30CC2