Well, your betta was most likely chasing the catfish because 1 gal is already pretty small for a betta, much less two fish...so his territorial behaviour really comes out in a cramped space.
As for the catfish, what type of catfish is it? It'd be a good idea to identify it, in case it becomes too big for the tank, isn't suited for living with a betta, or needs more of its kind. I think after those things are foigured out, you can consider getting other fish. Also, you'll want to cycle the tank first before you add a bunch of fish.
Puck (Yellow koi HM king) / Scar (White HM) / Salt 'n Pepper (Silver HMPK) / 'That fish' (Copper butterfly HM) / No name (White DT) / No name 2 (Turquoise/white marble HM) / No name 3 (Lilac HM)
Bo Peep (Cambodian VT) / Goldilocks (Yellow VT) / Joie de Vivre (Multicolour VT) / Lil' Peep (Blue VT) / No name (Dalmatian VT) / No name 2