How many shoes do I need for my indoor cycling studio?
You'll be pleased to know that you don't need any!
Although some studios will provide these shoes, it's not common practice (for good reason, as you'll see) - and there's a risk there's that 'bowling alley' experience where actually sliding your feet into some secondhand already-sweated-in shoes is just what you don't need after a tough day at the office when you're ready to unwind (and sweat). OK it's not as bad as borrowing someone's toothbrush (sorry), but it's not far off.
When new riders arrive, they're frequently low in confidence, and it might be years since they were last on a bike (if at all) and probably they've heard horror stories of indoor cycling (they're as prevalent as childbirth horror stories, due to low quality instruction).
If they're not sure what they're going to experience, possibly a bit nervous and not wanting to stand out, make a fool of themselves, or fall off - do you really want to insist that they fasten themselves to the bike by their feet?
Nobody's perfect, nobody's symmetrical either, and by the time you reach adulthood, those little wonky bits will be continuing to get wonkier. Some riders will just not get on with cycling shoes and will always be better off with flat pedals and trainers. Other riders may need their cleats placed differently - most riders won't have their cleats palced exactly straight.
What happens if cleats are wrongly placed? It can cause joint pain, numbness, and injury. Will your insurance cover you if your equipment is causing rider injury? Obviously with indoor cycling, we're trying to promote fitness, rather than cause damage.
Even if the above points weren't factors, would you be able to maintain these shoes adequately? Cycling shoe cleats will move - even after one session; do you have the manpower to check every shoe as it comes back in, make the required tweaks, sanitise, and make ready for the next rider? Would you be able to promptly replace the shoes - or will you need to make them last a bit longer?
How many shoes will you need? Hopefully you'll see that your capital is more wisely invested elsewhere. Get good instructors who know how to get the best out of your bikes and out of your riders, and you're golden.