When you've seen full grown neons or a large group of them in a large tank, you come to appreciate their behavior and needs more.
They get beefy for being 'small' and I wouldn't keep them in a 5g. 20g maybe.
For such a small tank, exotic shrimps such as tigers, cherries, etc.. would be good.
There are other tiny fish that are more suited for such a small tank, and can still be kept in groups such as Aplocheilichthys normani They don't look like much in pics, but when you see them in person, especially in a low-light nano tank.... the effect of their blue eyes darting between java ferns and under moss covered driftwood, is really cool