I used ISBoxer on Mischief for a few months. Never caught any vacations. I didn't use it that long, though. My guild finally died during VoA and I stopped playing. You won't get any straightforward answers about how it's treated. All I can say is I never got in trouble, and the few people I talked to never did, either.
The program was not user friendly at all for me and I spent many hours figuring out how to make shit work. But once I got over the learning curve, it worked well and was way more efficient than my truebox setup. I boxed 3 on my main machine and trueboxed a cleric.
If you're 3-boxing in this era generally the maximum potency trio is either Monk/Shaman/Bard or SK/Shaman/Bard. Whether you've got Monk or SK depends on what your goals are. That lead character is likely the "main" (raid character) in this situation as you'll need for them to tank and have the best gear. You can also do Berserker/Shaman/Bard and get something in-between (more tanking ability than monk, slightly less DPS). I did that for a while in the past and it was pretty solid, though now I wouldn't go with anything besides Monk or SK.
Paladin and Warrior are also possibilities. Like I said it all comes down to what your goals are and what you want to main. The TLDR here is that you need a character who can be upfront (tank things, be your raid character) that goes well with Shaman/Bard and you're solid. Wouldn't run Rogue, or a healer, or a caster, in this scenario.
As for the two top options, SK allows you to do a lot more content, while Monk burns through mobs faster. Do you want to push things by farming tough nameds, or do you just want to plow mobs for EXP? Do you want to offtank on raids or do you want to parse?
Like I said, Paladin, Warrior, and Berserker (hell even Ranger) also work, they just won't be as efficient as SK or Monk. SK can push the limits of what can be done, Monk will knock down targets the fastest.
Shaman and Bard, especially if they both have 2.0's, add an unreal amount of ADPS. Either of the "holy trios" that have three 2.0s done will be insanely powerful.
