"I don't think I would do so well as the leader of the insane ones." I curl up in a ball and start sucking my thumb, while my right hand pulls a rocket launcher out of my pocket that fires huge nukes. I shoot it straight at smylez.
All kinds of characters are allowed, long as they make some sense. I have a Ghost character, a Spectre, a Marine, a couple Customs....it's all good.
Is it okay to create a Ghost character?Depends on the RP. Some character types just don't make sense for certain RPs, though some RPs will allow almost any character including customs which are either hybrids of multiple units or just not in Starcraft at all.