If my experience is anything to go by you don't need to be particularly large or lavish to make a pretty good go of it.
I fly out of High Cross just north of Ware in Herts - the school is PSF, run by Alan Adams (who won't, I hope, mind me mentioning him here as publicity is publicity is publicity, I suppose!) out of what is essentially a farm strip. Portacabin office/lounge area, one PA38, and thassit. Two instructors.
Depending on whether it's winter hours or summer, at most he'll get 5 lessons (in two hour slots) a day.
The difficulty, I think, is structuring your prices appropriately - on the one hand if you run a smaller operation then prospective students will expect your prices to be lower than somewhere like, say, Cabair, and your running costs will in any case generally be lower. But on the other hand you can't be that much cheaper, because you still have to maintain and certify the a/c each year, take on fuel, ensure your ratings are renewed, pay the rent and all the rest of it. And your maintenance costs are likely to be more because you'll have to sub-contract the bulk of your maintenance.
Depends how much money you want to make as well as on what sort of image you think you need. The reason I use PSF is because I prefer the rather more relaxed, instructing-for-the-sake-of-instructing type approach than the I'd-rather-be-an-airline-pilot type. But others will prefer having more a/c, be reassured by instructors with nice uniforms and like the idea of operating from a nice busy airfield like Elstree.
Sorry, I'm rambling, the only point I wanted to make was that you don't need a fleet of a/c and a receptionist.
LB.