#1
Is gain boosting my SH59 - Pearly Gates a good idea ??

Whats a good gain booster ?? EMG ?? SD ??
Tone is all ...... well probably 75%, in your fingers.
The rest depends on your wallet's thickness !!

Keep the faith, baby!!
#2
Do you mean in terms of pickups, or an actual gain boost to your guitar? For pickups, anything active will usually get you more gain.
#3
gain boost switch as in Alexi Laihos.......
Tone is all ...... well probably 75%, in your fingers.
The rest depends on your wallet's thickness !!

Keep the faith, baby!!