Well, from experience, I started off my 10G without cycling it either. Stuck a Serpae Tetra and a Common Plecostomus in it only after having it for a week. So I started a fish-in cycle, essentially.
Barbs are cool, but they do tend to be a bit nippy and competitive. Not much you can do about that... The extra room will more than likely help, but probably won't fix the fin-nipping. If you're looking for nicer, more community fish and you're not too attached to your barbs, you might want to return them if you can.
One thing I had to learn the hard way is stay calm. Don't let the nervousness or stress get to you. Unfortunately, experiments with tanks like this take days, if not weeks, so patience is a huge factor.
After having had your tank for a couple months, your cycle is probably well on its way. I saw your other thread, and getting that test kit is key to making sure your tank is cycling. Don't fret about having put your fish in first before cycling, as a lot of people do that to cycle anyway. That way it gives consistent ammonia to get the filter going--just can be hard on the fish if they're not hardy enough. Seems yours are doing well, but once you get your cycle completed, your fish may become a little more docile as the levels of ammonia will drop and stress the fish less.
Have you been doing your PWCs?