I've been kicking this idea around, too: all the stuff I do (massage therapy, martial arts, yoga, lifting, training others) would really benefit from an actual facility, but I'm uninterested in drawing the gym-bunnies - too many people need real work, and all that overhead is geared toward memberships, not successes.
So: you really need to develop a sense of who you want to train in your place (general athletes, advanced athletes, the elderly, youths/teens, convalescents, bodybuilders, etc), what kinds of training you want to provide (aerobics, general fitness, free-weights, machines,, martial arts (or related), etc), what ancillary services (massage, yoga classes, pool, jaccuzi, etc) (and miscellaneous (juice in the fridge in back, or BYO or a smoothie bar? How many bathrooms? Showers? Lockers?).
From this, you can begin to build the kind of environment you want (in your head, at this stage), how much space you'll need, how much equipment, how many assistants you'll need, how much time you'll need to be there per day/week/month, how much you'll need to pay your people, how much utilities will run, the rent & build-out on the space.
Now, you can start on how many clients you'll need daily/weekly/monthly in order to keep the doors open, your help on-hand - and still pay yourself.
Did we talk about advertising? Promotions? Packages?
There's a lot to think about it. Thanks for bring up the subject!