This site isn't at all 'all inclusive' or the holy grail of truth by any means but it was immensely helpful to me.. It gives you the chance to change your ideas, numbers and species really easily to just get an idea of what could work.
I do love rainbow fish, though.. And there are a ridiculous number of sub species to look into. They will, however, be dull as juveniles.
GBRs are usually fine with tetras. I'd introduce them last, after everything else is established but it should be fine. I would avoid them, however, as they prefer higher temperatures than most community fish. They also prefer lower pH and people usually overlook this. They are also quite delicate and need pristine water with stable parameters. While they often do fine in the lower temps, that usually only last a minimal amount of time in these conditions.