I wouldn't put a betta with anything else in a 10 gallon, at least mid levels or top water feeders. loaches and plecos would be fine since they're bottom feeders. You can get away with a few, but i would not risk 10 tetras. Otos are okay, but they like groups and i would put at least 3 together if you want to see their best behavior. They also need algae to munch on as some have had problems with prepared food. I've heard they do better in cooler water than bettas too, but you could probably pull it off by sacrificing optimal fish health and happiness for your own viewing purposes, which many do anyways! (not bad mouthing it, just a neutral perspective).
I think whether or not tetras work will depend on the type of tetras. My betta did well for years with a small school of embers (tank was a 20g with 1 betta, 9 embers, 4 otos and an amano shrimp), but larger tetras could pose an issue.
Some bettas are more agreeable than others too, so the bettas personality will also be a deciding factor. Lots of plants also help, as tetras will have a place to hide, and bettas are less feisty when they too feel secure.