I agree with severum mama. I also have concerns about the betta with the danio. Danios are fast-swimming fish and they may harrass a slow-moving fish like a betta. And also as mentioned, danios need to be in groups, which would definitely overstock your tank. So, I would forget about the danios, but you could get another oto. Otos like to be in groups also, but if you got one more, the one you have won't be lonely. Any more fish than that, and I think it would be overstocked.