I would choose only one species and preferabley a mated pair. In a 55 gal
there simpley isn't enough space for two species of clown to co-habitate long term.
I would also urge caution on the choice of the yellow tang. Unless you have the intention of upgrading the tank size within the next year or so, the tang will outgrow the tank. For an FO
you still have plenty of other choices for equally colorful and personable fish, I would just suggest choosing ones with a smaller adult size.