10 gallon setup ... sound good?

Corydoras are not algae eaters so they won't keep the tank walls and plants free of algae. Otos are good algae eaters but most are extremely sensitive due to shipment and some are dying already while in stores. Also, Otos a schooling fish which I'd say probably needs to be around 5-6 Otos. But in such a small tank, the otos will be in competition with algae to eat.

I'd suggest getting some Nerite Snails instead of the Otos.

A lot of it will depend on the temprament of your betta. I had one that would not allow any tank mates. I had another that got on fine with anything I'd put in there.

Corys arn't really algae eating fish like otos are. I'm sure they nip at it every once in awhile but they don't have the suction mouths like otos. So go ahead and get the oto.

Ottos need 20+ gallon tanks. They need to constantly be eating algae that you probably wont even have. Over 3 corys are too much for a 10 as well, they still don't keep the tank THAT clean, so don't buy them just for that purpose. They also need grazing room. Get 4-6 pygmy cories, a betta, and something else-celestial pearl danios or nano emerald-eye rasboras would be nice.

I have to agree that corys are not a good idea for anything smaller than a 20 gallon, unless you are talking about the dwarf species. Even then they are not great cleanup fish...in fact, most fish are not. Every fish you add increases the total bioload (ie. the amount of waste both physical and chemical). Not to mention corys' mouths are not built for consuming algae.

The point about the otos is also good. They require quite a bit of algae to be fully fed and should not be left to fend for themselves. They should be target fed and have their own diet. And they really do best in groups. Even though I've found mine to survive as a single, he still enjoys schooling with my sids and I'm positive he would be happier with more of his own kind. If it weren't for the shoddy oto selection in my area I would most definitely get some more.