I used to run 9 gyms for the City of Edmonton so here’s a little more advice from those years.
As much as possible separate your “hard core” lifters from your “fitness center folks”. Different rooms are ideal, but even just different ends of the gym separated by shared equipment (cardio, selectorized etc).
As much as possible be efficient in your equipment use. Bench press stations aren’t a good investment, not when it’s cheaper and more space efficient to just have people bench in squat cages or on platforms with combo racks. Texas power bars are good for everything, then a few specialty (trap, SSB) to round it out. Do you really need a chinup station if your squat cage has a full set of handles too?
Combo racks, squat racks, and platforms are cheap (comparatively) and hugely cost efficient for what you can do with them. Specialized equipment like shoulder press stations and bench stations are more expensive.
Buy what you can used. People love new machines but your iron plates can be 50 years old and it won’t matter, check kijiji, Craigslist etc. Try to stick to one brand as much as possible but the plates don’t need to be new.
An elitefts adjustable box will work for squats, step ups, various jumps etc for less than having 10 boxes built. If you need them built get it done locally.
When it comes to trainers you can either make them staff or let outside ones in. Don’t do both, your staff will hate you and the workload will increase exponentially. If they’re staff pay them per session based on qualifications ($25/hr for basic cert, add $5 for a degree, add $5 for advanced cert etc, numbers are just an example). Charge more for their time as they get more qualified, just take your % or set $ off the top.
If they’re external then don’t try to regulate the number of sessions they can do. Huge work tracking that and guaranteed arguments about “it wasn’t a session, it was a friend”. If you’re going to restrict them do so by hours or day ($200/month for m-f 8-4, add $100 for evenings, add $100 for weekends etc). Just make their clients buy memberships. Also ensure that everyone has insurance in place and that it also covers you for what they do on your premises, also carry your own insurance.
Classes are a great $$ (crossfit, intro to weights, other snazzy names). Womens only classes will fill super fast every time since women love classes where men can’t attend. Tell the whiny me to suck it the fuck up when they complain but do ensure you offer a co-ed version. Don’t be afraid to cancel classes with poor registration.
Don’t teach classes or train people yourself if you can avoid it. Work ON your business not FOR your business.
I have about 1000 more points but those should do.
Again, feel free to ask questions, I did run 9 gyms.