Most of your arguments is based on the more advanced Ghosts. Nova wasn't a Ghost during the time of the Confederacy, she became a Ghost for the Dominion. And technically, you can kill anyone with psionics, even if you have a low level of telekinetics. Simple brain damage or damaging a major organ, then wait and let it happen. Also, one word: Spectres.
Oh it wasn't her that killed a bunch of terrorists when he family was killed in the tower?
I'm not saying it isn't impossible, but if you're going to play a psionic character you better a good reason. In other words, I am invoking GM fiat here.
If it's going to be mostly based from the Confederacy time, then Protoss and Zerg are pretty much constant hostiles. Base it from the Mercenary point of view, Zerg and Protoss could be allies or characters. Hence the stifling of creativity.
This mercenary point of view: please explain when this happens in the Starcraft universe. Last I checked, though may have been a while, you normally don't have the Protoss and zerg working together unless they were the bad guys. And even then, you still didn't have the Protoss and terrans working together too often except for special cases and those are after the events in Brood War.
As for Protoss being constant hostiles, they are hostile when they are getting shot at. Pretty sure you'd be hostile if someone was shooting at you for no reason besides being ugly (and no, I'm not calling you ugly).
Unless you have something constructive to present, or are willing to play, you'll be better off talking a gamemaster who is more inline with the rule of cool and not bound by plot. At least for a Starcraft campaign (SC2 might have a protoss character or three, but they'll still have disadvantages).