, angels do not belong in a 16g tank at all, and especially not with that many fish already in it.
I agree about adding 2 more neons to make a proper school.
Some other fish that could work IMO
would be black neons, glowlight tetras, glowlight danios (not glofish), and some smaller species of rasbora.
More plants is always a good thing IMO
. It really makes the fish colors pop out.