Nothing at all wrong with having a wide area coverage repeater on a hilltop to cover the entire district.
But it's going to be expensive.
Finding a suitable location, installing a tower, enclosure, power, equipment, design, permits, etc is going to be very expensive.
If you are lucky and can get a local city, county or other agency to host you at one of their sites, then it'll be a bit less expensive.
Many radio dealers would rather have you put on their own trunked radio systems. That makes them more money with the least amount of work.
And that might be a good option for your wide area stuff.
Depending on the sizes of the individual campuses, you may or may not need a repeater at each site. There's nothing wrong with simplex (radio to radio) if it does the job.
Larger sites may need an onsite repeater to get the building penetration you will want.
Linking sites can be done a number of ways. I understand not wanting to rely on the internet to do that, but building out your own mesh network can be expensive and require some serious upkeep. Likely each of your sites has some sort of internet connection, and leveraging that might be a good option. Spending some money on hardening the routers at each site with a large UPS might be sufficient.
But you'll never have 100% reliability, and even 99% is going to cost a lot of money. It's usually easier to train users on how to adapt in a failure.
I think you need a proper needs analysis done to develop the ideas from all the key users, then compare that to the cost. There are a lot of "nice to have" options, but it can get costly really quick.
I'd even suggest hiring a consultant to design a solution for you. While it'll cost some money up front, it'll pay off in the long run. As long as you keep asking individual shops to design a system, you're going to get stuck with whatever they are most comfortable with and whatever makes them the most profit with the least amount of work. That doesn't alway add up to a good solution.
A consultant can do a needs analysis and design a system based off that. Then you get what you need at a price you can afford.
Sales people can smell money. If you give them a budget, they are going to find a way to spend every single dime of that and then some.
If you approach it with a vendor agnostic consultant, you'll have someone on your side to fight some of the battles. In the long term, it saves money.