I've kept a few community tanks before.
I always liked keeping a large school (15-20+) of Neon Tetras when I had'em for their color, but there are a lot of beautiful Tetras (Glowlights, Congo's ect...) and I believe most of'em prefer each others (type specific) company.
Being as there's not alot of bottom in a Hex tank and what you have'll probably be halved for plants/structure, a smaller species of plec is a consideration, perhaps Bristlenose, Clown or a Zebra (this one likes a meaty diet) to name a few.
If you get Cories, get all one species and get atleast six (6) of'em, they are much happier and a'heck'of alot more fun to watch when in a shoal... They get very comical when in together

I don't know jack about Loaches...
But I'd say either do the Loaches, Cories or the Plec, Cories'll be more fun to watch
IMO...
Dwarf gouramies are nice, I liked the Fire Red dwarfs.
Tiger Barbs will harrass just about anyone if there's not enough of'em to keep the majority of pecking amongst each other.
If you do the Hatchets with the Gourami there may be a little strife being as they both like to cruise-n- hangout at the surface.
Just some of my thoughts...
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