Cherry Barbs are a nice barb you could have in a community. You could swap them out for the Harlequins.

Otherwise, a large all-barb tank sounds great. You could have 10 Tigers, 10 Golds and 10 Greens. I'm not 100% sure so don't quote my on this but I think you could keep a single Red Tailed Black Shark with the barbs, it should be able to take care of itself. That or a Cichlid of some kind, like a Convict or a Sajica cichlid to add a little personality to the tanks. Most cichlids make good wet-pets are there are lots out there which would work in a 55g with a large school of Tigers.