Some shrimp are fine, such as wood shrimp, also known as Bamboo shrimp or Singapore flower shrimp. They grow big enough to not be edible and filter feed so they wont harm the fish. Angels and pretty much any cichlids besides rams are a no-no in your tank. I love blue/opaline gouramis, and they get along fine with Bettas. I had 2 blues and a male betta in a 10g once and they survived perfectly for 4 years! I also had a pleco in there, as this was before I knew it was even called a pleco. I just called him a "sucker fish" lol, the n00biness.