More danios, definitely, but personally I would avoid mixing types. I would stick to zebras. More of one kind just looks better in my opinion.
More black skirts and neons, yes.
the bristlenose, yes.
corries, yes.
Snails, shrimp, and livebearers of any sort I would just avoid. But that is me...
Maybe a pair of pearl gouramis. Beautiful and peaceful fish, and would stand out amongst the fish you have.
Maybe one of the larger gouramis, such as opaine, but I am not sure of their aggression.
Or, you could happily home a pair of keyhole cichlids in there. They are not especially colourful, but have all the wonderful cichlid characteristics, minus the aggression. Mine are currently spawning and are still not viciously attacking other fish.