To answer about mixing Spixi and Nerite; I have one tank with a number of Spixis in it, and it also has a few Nerites and a small number of nuisance ramshorn and bladder snails. The Spixis keep those last two from increasing in numbers.. though I don't think there has ever been a day there were not a few of the nuisance snails in there. The Spixis themselves don't lay a great many egg clutches, [ underwater], so they don't grow in numbers very fast either.
The Nerites, so far as I have observed, have not been bothered much by the Spixis in this tank. I think they are harder for Spixis to catch.. they have a different arrangement with their operculum than snails like a Mystery. Spixis seem to greatly prefer snails that have no operculum, like the ramshorn and bladder snails. But Nerites are not immune from attack, and if there were no other snails available to prey on, a Spixi might succeed in taking a Nerite.
So, personally, I don't think I'd keep one of each in a small tank. Too much chance the Spixi would kill a Nerite. But shrimp actually do perform a pretty reasonable job of eating algae, but with them it's more numbers that count. Just a few cherry shrimp won't make a big difference to algae.. neither will a few Ghosts or Amanos. But a small colony would consume a fair bit of algae. Even in a small tank, you can have quite a few shrimp, a dozen cherries to begin would give you a fair colony after awhile, they nearly always breed pretty freely. Six would take a bit longer, but still, some of them will be female and have babies.
If your main concern is that you don't want any pest snails, there are ways to manage that, by dipping any new plants before you add them to the tank. That can reduce the chance of nuisance snails to near zero. If your main concern is controlling algae, there are ways to reduce that too, by controlling how much light is available and how much food.. that is, nitrates.
But for eating algae, best bet is a Mystery or Nerite.. and I'd get a couple of Nerites, as they aren't that big and they are slower than a Mystery snail is.
Snail or no snail, I'd get the cherries, they're fun to have, fairly hardy and they do breed easily most of the time so you get replacements.
