Good point on the ability scores.
I like the Strength, Dexterity, Intelligence & Charisma idea better.
Appearance being a trait/advantage makes sense, it works that way pretty well anyways in GURPs.

Difficulty, I would rule go a bit D&D logic. It should take 4 to 5 'encounters' without rest to exhaust your resources and put you in huge danger.
Giving liberties to do less encounters in a day but make them more challenging for more intense RP's.

Though players fighting something equal to their own power level should be rare moments, since each of those have a 50/50 chance of total player death or failure.