Instead of Neons try Cardinals ...they to me are a much prettier fish. You can also get fake neons and several other varieties that are nicer than the neons.
I've just had 6 females guppies give birth and my tank is full of fry. I'm lucky that most of my gals are not canibals. If I find one that is .........well she doesnt stay around long! I rehome her. Alot of show breeders kill them *WHACK* ugg I just couldn do it. I'm no expert but I do read alot about them. I think your livebearers will give you alot of pleasure. Mine certainly do.
Oto Catfish are nice, because they stay small. They should be bought in 4's at least. Cory Catfish are also a lot of fun to watch, but are a bit larger than Oto Catfish. Mystery Snails are good at eating algae too, but go to Apple Snail to make sure you get one that doesn't eat plants. The ones they sell at PetSmart don't eat plants.
Are you looking for something to contain an algae problem, because a fish is not going to solve a huge algae problem. The tankmates I mentioned are good for cleaning up wisps of algae, but if you have a serious algae buildup, the tank is getting too much light and is high on the bioload. If you have questions about that, please feel free to ask, but my recommendations for algae eaters are some of my favorites in the tank. You will probably have to provide algae wafers to suppliment their diets.
The fish would be for very small amounts of algae. I don't have a big buildup. I wouldn't have to worry about snails eating plants as I have fakes. Really what I need is something small that can be kept in 1-2
While Plecos are good algae eaters, they get quite large. Even a Clown Pleco, which generally only reaches about 5" requires quite a bit of room because of the waste Plecos tend to generate. I wouldn't put a Clown Pleco into anything less than a 30 gallon unless he was one of the only things in the tank.