Is two Otos and 1-2 ghost shrimp to much for a 5 gallon tank with a Betta already in it?
The one inch of fish per gallon thing is BS, you can have a ten inch oscar in a ten gallon tank. Ten one inch fish in a ten gallon you likely over stock it as well, but that is only 2 of many reasons you should not go use that "rule" Oto cats do best in a group of 5 or more. Otto cats or usually wild cought and more sensitive then the average fish. The are strict herbivores, they NEED to be added to a tank with some algae growth. Then you can try to ween then on to some herbivore pellets, spiralina , seeweed, Get a 20 gallon tank, get it fully cycled - 4-8 weeks, and let some algae start to grow, then think about keeping the wild cought otto cats. or perhaps a shoal of cories. you would not have to worry about them not eating store bought foods. "otos do not always adapt to commercial foods"
Do not buy any more fish or live animals for 6 weeks. Anything you add during this period will be less likely to survive. So just wait. The tank will be healthier then, and you'll have a chance to learn correct maintenance.