Looks:

I don't headcanon Starflight any differently from the WoF Wiki. Except for the fact that at the back of his blindfold, all his friends left a tiny signature of their names as a remembrance.

Sexuality:

Starflight is straight. He has never had feelings for anyone other than Sunny, and Fatespeaker.

Voice:

Dipper Pines / Gravity Falls

Other Headcanons:

When Starflight went blind, Clay went to save him and ended up with a fringed wing. Starflight lost some claws and a bit of his wing, but can still fly.