Common-looking TSN baby.
It will change heavily from 3" to 6"-8" and the pattern will keep evolving strongly until 2' and still substantially after that throughout its life.
They are unfussy, usually. Frozen-thawed is almost never refused. He is most likely adjusting and will start eating soon, within a week if all is good.
They like cover until a bit larger but usually stop hiding after they reach 8"+, if no bullying, right lighting, etc.