#2
for blues I would go with a les paul. For heavy riffs I would go with an sg. imo les pauls have more a richer midrange which sounds better for blues. SG's have a chunkier sound which I think sounds better for heavy riffs. i think sg's have more versatility. Both are great guitars, you should try them out for yourself tho because everyones ears are different.
#3
They sound pretty similar, depending on which model you get. I personally hate the SG horns because they dig in when you're doing large stretches or anything past fret 14. I only play V's now, so my opinion doesn't matter. But here's a rundown

If you suck like Slash, get a Les Paul

If you suck like Angus Young, get an SG

I you rule like Zach Wylde, get a Les Paul

If you suck at an annoying level, even after 40 years of playing live like Angus Young, get an SG

Basically... to hell with Angus Young... those devil horns make you look lame.