I applaud you for taking in a betta! There needs to be more people who are willing to rescue those little guys from those deathcups.
He really does look stunning!
I'd have to agree with Bettaqueen on waiting a little bit before moving him over to a ten gallon. I have two rescue bettas and I had to move them very slowly to larger tanks over time. Some bettas, when put under stress, become fin-nippers.
Good luck with the little guy, and congrats! It's obvious that he's being well taken care of.