Hi, 40L is a small tank for marine fish. I definately wouldn’t advise even thinking of putting an anemone in that space.
You could probably get away with a normal clown fish (they’re fascinating to watch and you’ll soon see why their named appropriately), a blennie or 2. A shrimp if you like them, but you’ll want some hermits in there for sure. It’s kind of a small space for 2 clowns.
I started off with a 40L and had a firefish, bicolour blenny, 2 cleaner shrimp, a goby, hermits & live rock. I’ll post some pics of my tank later.
If you want something interesting i’d probably choose a pistol shrimp and goby pair, that symbiotic relationship is cool to watch.
Just don’t rush things in this hobby