Well as far as the pleco, I probably wouldn't consider it because they are poop machines, the bio-load would be a little strenuous for a 10 gallon. I would suggest, if you can, find a dwarf cory cat as they nibble on algae, if that's what your worried about, and also sift around in your substrate. However with all cory cats you have to keep in mind that a smoother substrate is good for their barbels because if you have a sharp gravel it can hurt their little feelers and make it not feel nice for them. So I would just recommend sand for them or some smooth river rocks for a substrate if you went with them. Sand is actually a lot more simple than some people think it to be, but of course it all comes down to personal choice and funding :D here is a great way to clean sand if it comes to it http://www.youtube.com/watch?v=d-XB0bwtZh8
As far as shrimp with your betta, it depends on the betta. Some will coexist with the shrimp just find but others will see them as a tasty treat and so you'll have to experiment with this. If you don't know how your betta will react then I would try one ghost shrimp first and see what he does since the cherry's are a little more expensive. Same with the frogs but I've never owned them but I've heard some stories about frogs and betta's not getting along. But I would wait until someone with more experience with this to comment.