We never even thought about Assassin/Op, we were kinda set on the whole same planet thing. How well do you think those two would perform? I can see there being quite a bit of CC in there, might be able to take two enemies out of a fight for 60s? That might make heroic 4 and some flashpoints (if we overleveled them) possible.
Well, starter planets are about 4 to 6 hours. Should not be that big of a deal once you get to Dromund Kaas. And it's Certainly possible to solo every levelling FP with tank+healer+2 up to date DPS companions (as long as you point them in the right direction, ergo the focus fire target).