Noob inheriting a full set up

[Cell]

I'd do a 20-30% water change today and cautiously say don't sweat the API ammonia positive too much provided the fish are still acting normally, and yes, the clowns chilling by the filter is completely normal. This is assuming the existing rock and biomedia was kept wet when moved.

The Tunze 3155 ATO is the gold standard, but not exactly cheap. Still, it's highly recommended.

Cleaner shrimp is fine in a 20.