I assume you've acquainted yourself with the info in the linked threads that answers your questions. As far as my personal experience, I've bought a pair at $55 each. They were 5". In half a year they were 10". Fast growth but less than reported in the linked threads above by others.
As for your fish combo, as long as the sizes remain similar and small, you are likely good, albeit I had my FL gar bite anyone in my community tank while he clearly could not fit them in his mouth. Silly fish. Had to separate.
Such a diverse community will grow at different rates to very different final sizes, so keep a good eye.