Nice! 12 isn't too much though? Not sure how big they get.
I have a question for you. Are sparkling gouramis not like other gouramis? I'm talking aggression-wise. I have peaceful community, and wouldn't want to disrupt that. There is a GBR in there, but he doesn't bother anyone.
Sparkling gourami are reserved ,almost secretive .Is wise that you chose the threadfin's for they are not nearly as aggressive as some other's at feeding time which would make it more difficult for the afore mentioned gourami to get food's as it fall's to substrate.