I am very new to keeping a Betta so my imput is from a well respected member of this forum...
Apparently, a Betta's stomach is roughly the size of its eye. That's not to say though that he wont try to fit an amount of food the size of its head in it.
I was told to feed my new boy every other day and then only a couple of pellets or a couple of bloodworm.
This is to avoid swim bladder problems.......
Fish in the wild permanently live on the very edge of starvation and have evolved to cope with this (allegedly)