Is my aquarium set-up ok?
You need an air pump and air stone as a minimum. Start the tank and add the algae balls first. In three weeks get the snail. I'd add a ghost shrimp too.
Is the snail the only animal? You'll need some biological filtration and water movement. One thing you can do is add an air pump with an air stone, then take a small mesh bag and add some ceramic media rings to it, then use an elastic band to tie it around the air stone so the air bubbles flow through it. Snails are sensitive to nitrates so fully cycle the system. The little DIY filter I described will work well though.
It really depends on the price (of one filter), If I were you I would buy a filter anyway, just to be safe. I would never trust a single website either. Sorry though because I'm not good with snails only fish lol. If you want me to rephrase that I can for you.