AFAIK, Spotted Cardinalfish will get far to large for a 10gal tank. 3 1/2in, aprox full size. maybe as a younger fish, but when it gets larger, no, it would be to large. I once saw adults at my LFS, they would have been cramped in a 30gal tank, let alone a 10gal... stick with smaller fish, judge by size if nothing else. So yea, I don't recommend for a 10gal tank.
Other then that, your tank is looking very nice. I would go with a stock of gobie/shrimp combo with a pair of
Firefish! That would look nice, and none of those fish are aggressive or get to large for a 10gal. Good luck!