First of all, what size tank do you have?
If by zebra fish, you mean zebra danio you need more of them to make a small school of 6+.
Some pleco's quickly outgrow tanks and can get to be the size of an adult forearm.
And finally, rainbow sharks can be aggressive and they're known to bite fins. Not suitable for a betta tank.
Before adding anything else, I would go get a 2.5 kritter keeper and heater and remove the betta before he gets hurt or killed, secondly, get some more danios for the one you have. The ghost shrimp, without adequate plants cover may be susceptible to being eaten as well.
You can't just have 1 of every fish you like. You need to research their individual needs.