I personally feel that the option of having all of the powers unlocked from the beginning would be pretty OP. Considering that it's likely they already know how to use all of their powers, it would feel like giving too much of an advantage. I'm all for limiting to a maximum of two powers at the start though, like Unraveller's character. Especially since he picked two of the weaker powers as well.

A good example would be like if in DnD, I had a sorcerer that not only had a mastery in pyromancy, but also necromancy, and allomancy right from the start. It gets rid of that sense of accomplishment you recieve from building that character up and unlocking those other mastery's with everyone else.