Hello and welcome to the forum. Firstly what is the tank size. I would avoid the vampire crabs as they would nip at the pleco and gouramis. They also require a land section of the tank.
If you want something unique then you could go for sword tails. Their not too rare but the males look quite cool and different. If your concerned about nipping then are you sure your barbs aren't nipping your gourami.
Hi I have swordtails in there at the moment and to be fair I haven’t noticed the barbs fin nipping when I was at the shop near me the fella in there said they should be fine so I took his word for it but like I said I have never noticed it
If you have swordtails then another fish could be albino cherry barbs. A bit rare but very unique colours. Should be compatible with current stocking. I am quite surprised the tiger barbs have not nipped the fish, they're notorious for nipping.
Never, ever believe anything a shop worker says. The majority of them are trained in how to make a sale not in how to care for fish. Even the small independent shops give poor advice.
I will make sure I now keep a proper eye on them now just in case but not noticed it yet
