First, welcome to Tropical Fish Keeping forum.
Responding to your questions...a 55g is insufficient space for the Red Tailed Tinfoil Barb, as noted in the profile [I believe you are aware of our profiles, second tab fro the left in the blue bar at the top of the page; if the name used in the profile, scientific or common, is used exactly the same in a post it will shade].
Rosy barb in a group of 6 minimum or more preferably is OK. But notice the cooler temp this species needs, and the RTS is slightly warmer.
All barb are shoaling fish, meaning they need to be in a group for one or more of several reasons.
I would not mix gourami with the RTS due primarily to water flow issues, as noted in the respective profiles.