[@frapet]

its an interesting base concept.

The first impressions are that the character could grow into something interesting.

On the subject of his ambitions and behavioral style... He has ambition, but keeps it tempered, concealing it beneath a shell of servitude, but does not truly plan anytime soon to gain a higher rank than apprentice? Remember, in the empire you need to seize power to rise above a certain point.

Anger is but one of the ways of wielding the dark side, and even that can come in both controlled and uncontrolled forms. there's the methodical anger where you work to ruin someone's life, and then there's the mindless rage. We're guessing that his rage is hard to bring to the surface, and that he values control?

Have you given any thought to whom he serves?
Darth Nyiss doesn't really want (or need) an enforcer (which is kinda what he looks like he'll be), but there are other Sith that might want one. Even apprentices can have apprentices after a while. There's a few invisible divisions within the rank of apprentice, and of course titled apprentices are the highest tier of apprentices.

As Sep said, we'd really like more flesh in the bio. But its better to have a sparse skeleton at the start and fleshing it out than to have pages of stuff that doesn't fit and has to be replaced. Try building something around what you have in the other sections. Something to justify his skills and such. You can refer to major moments, like how he was discovered to be force-sensitive.

Force powers can also be built in once you have a clearer grasp on the bio, as the best way to assign them is to have them reflect the character.

Don't hesitate to ask questions or to ask for help.