you should get some kind of betta pellets for a staple diet. if you keep feeding him the same thing, he will eventually accept it. also, be careful not to feed him too much. food labels say that you should feed as much as the fish will eat in a couple min, this is untrue for the betta. the betta will eat as much as possible, and if you feed him too much he will literally explode!
nice tank! i would keep filter. i'd also put in a ghost shrimp, they are really interesting to look at. but some bettas will eat the shrimp and some will not.
your betta looks beautiful too! common ones are not just called regular ones, i think they are called veiltails. i'm not really good with fish names, i keep accidentally calling one of my cichlids cocoa, my dog's name. lol.
how much did you spend on that kit?
o, almost forgot. if you feed him really rich food, like blood worms, for a staple diet he may get constipated and could die if not treated. you can avoid this by just feeding him such foods as treats, and you can remedy this by giving him peas.