All snail bio-load are big!! Shrimp are small, however the bigger the shrimp the bigger the bio-load.
For a 10 gallon with a Betta and 8-10 schoolers, I really don't think you should get anymore fish. Your tetra's will stay more towards the bottom where Cory's would be so you don't want too many fish on the same level. It starts to overcrowd. Besides, Cory's add more to the bio-load and they sure do poop a lot! Same with any and all algae eaters, all of them poop the most out of all the smaller freshwater fish. So I'd just stick to what you got and that should be good