The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
You could add some non-nippy tetra species but I suggest not adding a dwarf gourami since you have a full size one already. The 2 could possibly fight and IMO is not worth the risk.
Angels mature at about 8 months and honestly the only way to be 100% sure of an angels sex is to see what it's breeding tube looks like when spawning. Many people take educated guesses using things like a forehead bump in males but that isn't always accurate.