Congrats on the new betta! Tanks and bowls are both fine, but make sure the bowl is big enough for him to have plenty of room to swim around. A tank would be great as well. I would recommend 5 gallon tank (a 10 is good too but for one fish a 5-gallon is fine). I have 4 bettas living nicely in a 10-gallon tank, divided with the same divider I use for the gerbils.

I feed my bettas three or four flakes a day. They do fine, but I've heard of people who give them more. If they don't eat it, I scoop it out. What you are planning to feed him should be fine for him.

I use fake plants for my bettas, and they like them. I think there are some real plants that can do damage to the fish if eaten. I'm not sure though..

The water question.. I'll have to ask my dad about that. I'll get him to post here when he gets up for work.

No tank/bowl-mates whatsoever. They will fight and kill each other. But if you want another one you can divide up the tank with a clear tank divider. I like this idea because the bettas can see and interact with each other, but they cannot harm each other. And if that is your decision, make sure that there is no way the bettas can get through to the other side. I had an accident where Ocean escaped from his section and into Bubbles' and he bit Bubbles' tail off (Bubbles is still alive today, and his tail has grown back nicely). Luckily I noticed before there was any further damage done.