Large refugium??
 

I'll soon be setting up my first saltwater aquarium, and I'm trying to plan out what fish will go into it. If I were to buy a 90 gallon tank, with a 75 gallon refugium, would that allow me to add anymore fish than if it were a 90 gallon without, or with a small, refugium? I'm thinking mostly of small community fish.

It seems that the extra water capacity of the refugium would allow me to add a couple more fish without overloading the system, but I'm not sure if that's right. I don't want the fish to be cramped. (Filtration would be live rock & a wet/dry, if that matters.)

Yes, it would allow you to expand slightly on the total stock you wish to keep, however it will not necessarily allow you to keep fish that require a larger system