Yeah, you don't need live plants. Silk plants (ones made out of fabric) and plastic plants that aren't sharp are just fine. Run your plastic plants across a pair of pantyhose. if they don't snag or tear, the plants are safe to use.
The amount of plants is up to you, but bettas do like coverage, so be sure he has some sort of plant and decor that he can hide in if he needs to.
Zebra danios could be a little overwhelming for your betta, but I guess it depends on each individual fish. They like to school so you should get about 6 of them.
Do not put a female betta in the same tank without a divider! They can and will fight.