Small, multiple meals per day is a lot better/healthier than one larger feeding a day - by nature they will eat throughout the day whenever they find food. I prefer doing multiples as if I fed the amount I feed mine all at once then it could cause digestion troubles.
The type of foods most popular are New Life Spectrum and Omega One Betta Buffet. But really what you are looking for is a high protein based food - I prefer 48%+ crude protein, but a lot of foods are 43%+. Some meat/fish is very important.. you will want to make sure the first ingredient is at least some sort of meat/fish.. even the "fish/meat meal" is fine, it's just a mish mash of parts of fish/meat.
As for the amount - will depend on your fish. If he is very active (sometimes it takes a good amount of food to become active) then you will want to feed him more/more often.
I say start out with 3 pellets per meal, twice a day and see how he does.. if he is active you can bump it to 4-5 pellets per meal.
Some slight roundness to their tummy after eating is fine - you just don't want to make it too large. If you notice he gets really round after eating then you can cut down the amount he eats, or cut down the amount per serving and feed 3x a day instead of 2x.
But you will be able to tell by watching him how much he can eat with no trouble.. also keep in mind the higher quality the food, the less they need as there will be less filler/waste and they will absorb more of the food the better quality it is.
I still feed a ton, even though I feed some of the best food out there.
No, the foods won't expand and kill.. over feeding of poor quality food will cause bloating/constipation. Probably why I've never had to deal with that in any of my fish in the last couple of decades - I feed my bettas anywhere from 8 - 20 pellets a day (sometimes less when I feed frozen/live/homemade food that day), with no problems to their digestion.
Don't need a day of fasting, but it won't hurt them.. sometimes I will skip a day or feed only once (smaller amount) to give them a break, but that is largely a fish by fish case - my "pet" bettas don't get nearly as much as my breeding stock - but they still get roughly 10 pellets a day with no problem.
I don't suggest feeding as much as I do - I know my fish and know each of their limits and will often work them up to the amount I feed. But I'm just letting you know that feeding 1-3 pellets a day (or less) isn't needed (nor do I recommend that little of feeding).. their stomachs may be as big as their eyes, but like all stomachs, they expand. As long as the fish is active (a good flaring session a day will help) they should be fine digesting large amounts of food with no trouble.
Again, depends on your fish.. some fish (especially it seems like CTs) won't be able to handle a whole lot of food at once, but you will be able to tell after a week of feeding and experimenting to see what is best for yours.