Questions about otos, albino bristlenose plecos and ghost shrimp! Plz answer!?

How many otos can ft in a 10 gal with 3 male guppies and 1 female betta? Do u have to have to have to have a group of 4-6? Why not 3 2 or 1 there sucker fish, they don't need a school like tetras, right? Basically I want something for my 10 gal and maybe 5 gal if anythin can fit in it with my male betta to eat all the algea of the sides of both tanks. Also a question about my albino bristlenose plecos, I got the 2 in my 40 gal at the same time and one of them is like 2 times bigger, is their such thing as dominance between the to? Is the bigger one a male? Is it a female? Iv had them for about 2 weeks now so they haven't grown any whiskers yet if it was a boy but it kindof looking like one has whiskers. Also the bigger one is bright and the Other smaller one is dull, is that also cuz of dominance or is it just not getting enOugh food? Do I have to buy algea wafers for them? If I do, hoW can I keep my ghost shrimp from eating them because thy already eat my Cory's food! Is their any food that is specified to feed shrimp!?