A 5g set up would be great for a betta! I agree Red, everything sounds good so far.
As far as the corys/otts, Some betta will accept them as tank mates, some won't so if you decide to add them, have an alternate plan in case there's any signs of aggression.
From what I've read here on the forum, corys and ottos like to have more of their own kind to feel comfortable and a 5g may not support this.
That being said, there's exceptions to everything.
Good luck.
Edit: This is a terrific thread to read about betta care.
Welcome and Betta Care Guide - Please Read First!!!