Can I ask how many hours each aircraft flies at your school? At ours we had as few planes as we could and a maintenance company that loved to charge and nowhere else to go. I agree, I would love to remove useless instruments or replace them but it needs to be sensibly economical.
The club operates 4 aircraft, and we do just under 2000 hours a year. Mind you, that includes solo rentals from members, instruction is only about 1/4 of that.
The check-out is pretty thorough : there is a 40-question quiz which you don't pass unless you have read the POH and understood it and then there's an additional 30 questions on the avionics. It's not a guarantee for renter's competence and care, but it weeds out the "cack handed".
As for the temporary instructors thing, the problem stems from the fact that as a PPL(A) instructor unless you're flying significantly more than you're supposed to it's actually very difficult to make a living out of it because of the margins we work under. Career PPL flying instructors are rare, rarer than rocking horse dung.
None of the PPL instructors are full-time. All of them have real job, or are retired. But as long as you create an environment that keeps them happy and you eradicate the odd-ball that doesn't understand
(a) instructing; and
(b) customer service
I don't see anything wrong. Availability is pretty reasonable.
The things that are free however, like treating your customers properly, calling them if you want to move their slot/ talk about cancellation giving a reasonable brief, a warm welcome and free tea and coffee are a bloody good start.
Yes, yes, yes and yes.
a maintenance company that loved to charge and nowhere else to go.
is one of the cruxes that need to be addressed. If you're dependent on some larcenic EASA part M paper pusher annex parts docs falsifier, you're doomed.
We have some competition at our place, which obviously helps. The only alternative is to incorporate a maintenance facility in the flying club / school. That is the way most US FBO/flight schools operate.