Just Throwing It Out There

[Chad]

I think in the 55g you could get away with;

8x Black Widow Tetra's
8x Red Minor Tetra's(Serpae Tetra's)
8x Cherry Barbs(if you want to replace the Neons with something or you can up the above numbers to 12 instead)
1x Rainbow Shark
3-5x Mollies(all male unless you want babies although most of babies would be eaten in an instant with the above stocking)
&
1x Opaline Gourami.

Sound about right.
I love the way rainbow sharks look but don't care for their behavior much. I tend to like cory for my bottom dwellers. But that's a personal thing. I love serape and cherry barbs are (to me) the best barb you can get. Mine were always hardy with a minimum of picking.
Mexican Sail-fin Molly are among my favorite FW fish to be sure.
Again a personal taste thing but I would rather have something like a sunset wag platy.
I think a 55 gallon tank is a great choice if you can get it. I find that tank to be a good size to do lots with. It's even a good starter size for a marine tank if you ever go that way someday.

 

[Lunar Jetman]

I've never kept gouramis on their own but I guess my tanks have always been big enough.