Their stomachs are only as large as their eye, so you only feed them a few pellets at a time to avoid overfeeding. They are piggies. You can feed them twice a day.
Silk or real, doesn't matter. It's really your preference. Avoid plastic as they can hurt the fins. If the plant can be run down a pair of pantyhose and doesn't snag, then it's OK for your fishie. The betta will be happier with a plant (real or fake) or two or three so he's got a place to hide. He'll feel more secure. Some like caves.