Really, I can't think of any fish that belong in a tank that size except for possibly
a Betta or perhaps 3-4 Least Killi fish.
But an Amano shrimp might be a nice combo/w those Least Killi fish and would eat the algae.
No. You need four ottos at the VERY least. Do not get ottos.
Nerite snails, amano shrimp, or cherry shrimp. Those are your only good options.
If the tank is very heavily planted, you can have four ottos and nothing else.