3 or 5 otos would be great, they're not hard to care for it's just that the majority of them (probably about 80%) die within the first month that you have them, but if you can get them to live for longer than a month they'll generally live for years. the problem is that they are wild caught, and don't get any vegetation (algae, fresh veggies, plant matter, etc) from the time they're caught until the time they get to your tank (unless the
LFS ensures that they eat which most wont). because they don't get any veggies there is a certain kind of bacteria in their stomach that will die without it and cause them to starve. otherwise they're amazing little fish and really do a number on algae
you could also get some nerite snails, their eggs will only hatch in brackish water so you don't have to worry about 100s of baby snails in your tank
i'd suggest getting one more glofish and then having, for example
6 glofish
3 platies (if you have two males, i'd get another male, if you have two females, i'd get another female, if you have a male and a female, i'd get another female)
2 german blue rams (really pretty fish but can be very sensitive to water parameters, make sure your tank is very clean)
5 otos
and that would have you pretty fully stocked