I have been 2 and 3 boxing for a while, though dont use a lot of sophisticated methods. If you use 2 machines for 2 boxing, that is fine. If one, then need to get into ISBoxer as follow becomes a little problamatic.
As to characters, I have a cadre of characters, and find a caster/tank type as always the best combo. I start them in pairs, leave the mines immediately, get mercs, then die to return, and do all the quests in the mines and you level quickly. Getting to about 50 is not too bad, and then the going gets slow. Using higher characters does help, but levelling more than 2 levels a night is tough. From 65 on it is really slow.
My main combo is a DRU (82)/RNG (83) with JV mercs. I do ok in Old BB and Kith but FOS gives me problems with the names, as they rapidly aggro onto the DRU, and summon him, so goodbye DRU.