I want to paint art on my walls. See the attached photos for examples. If anybody has done this before, please give me some pointers.

1) What kind of paint should I use? I'm guessing Behr's Premium Ultra would be easier because it has primer mixed in.

2) How do you protect the art after its done? I suppose it needs to be sealed. In case somebody bumps into the wall, I'd want to clean off the smudges easily instead of having days of work ruined permanently.