I would not recommend gouramis for cycling a tank, I would recommend livebearers or rosy red minnows. I think the LFS may have been trying to push a sale.
I'm sorry, but keeping an opaline gourami in a 10 will not be a happy setup for him long term. Try a honey gourami, instead. I'm sorry, I know how it feels to return a fish you really like.
If you were to get a honey gourami, you can get a group of up to 5, add some otocinculus catfish, and ember tetras once the tank is cycled, and you'll have a tank with great color. Typically having more of them keeps the aggression down, but the tank is still to small for opalines. A 10 gallon is still considered a nano tank, so keep on the nano side.
Hope this helps you!
This is the honey gourami:
That looks