Ah, I see you are now hooked in the hobby, just like the rest of us.
That first tank we all think will be big enough for what few fish I want, but then...more and more tanks.
A caution on the otos. First, they will only eat common green algae and diatoms (the brown that usually appears in new tanks during the first 2-3 months, then never again). So they will not touch the brush stuff you mention. Second, adding any fish to a tank solely for a purpose like algae means you are increasing the bioload and will be that much closer to a "full" tank of fish. OK if you really like and want the fish on its own merits, but not OK if it is solely there to handle a problem--esp since it probably won;t. Third, otos are shoaling fish that need a group, minimum 3 will work. And fourth, when introduced to "new" tanks they frequently do not last unless there is plenty of the algae they will eat and the thank is fully cycled at the minimum.
Snails do eat algae, just be careful which you get. I like the small ones, Malaysian Livebearer snails are excellent as they burrow through the substrate keeping it clean. I also have pond snails and bladder snails. None of these three will harm plants. And they do a tremendous job of "cleaning up" stuff, not just algae.
On the numbers, I expect you have them correct. Nitrite at 1 is serious, but at 20 you wouldn't have a live fish (or anything else) in the tank. Do a daily partial water change, 50% with a good conditioner, if you continue to have nitrite above .25, it is very toxic long-term as it deprives the blood of oxygen.