I have 4 gouramis in with 8 tiger bars and they pretty much leave each other alone. I was concerned that the tigers would nip at the gouramis feelers but I have never witnessed that yet. Occasionally a gourami will chase away a tiger from his territory though.
I would have to agree that the tank is probably too small to handle those two fish types together. You would really need to look at least at getting a 20 gallon before I would chance those two. I would stick to one or the other. And yes, barbs seem to really like that magic number of 5 in a group minimum to keep the aggression within the family.