Yes, that is what flaring is.
As far as flakes.. unsure the number.. I don't feed mine flakes, they tend to cloud up the water if uneaten, plus could cause bloating if overfed. Pellets are easier, can see just how many each are eating and can take any uneaten out easier.
But a small pinch a couple times a day is okay I suppose.. hard to describe how much a pinch is (not all flakes are big and they crumble so hard to say 3 or 4 flakes, etc).
And no on the goldfish flakes.. bettas are insectivores/carnivores and require a different balance in their diet then goldfish. Use betta pellets, frozen foods such as brine shrimp/blood worms, and on occasion betta flakes and freeze dried.