If you want big fish, why do you have to plan 10 gallons?
Congo Tetras when kept in a shoal of 6 will need 55 gallons minimum no matter what size they'll be. Juveniles will still grow considerably.
The same thing applies to rainbowfish(larger species).
They need large swimming space as opposed to the small areas in a 10 gallons.
For 10 gallons tank, only a betta, smaller tetras, harlequin rasboras and cherry barbs will fit. If you want bottom dwellers, try otos and cories. For surface, hatchetfish will do but ensure you have a glass cover as they jump.
For unique fish, threadfin rainbows(Iriatherina werneri) will do.
Ensure that they are the only fish in the tank alongside with perhaps, harlequin rasboras but threadfins are best kept among themselves. Make sure you don't keep them with fin nippers.