That is going to get really expensive really fast at that site, especially if you are running them with redundancy. Although, if you have zero fab skills, it might be the way to go.
Lets see if I can explain this clearly enough.
If you aren't concerned about looks and feed the system from a centralized tank that is above everything else, you can vastly reduce the cost. You can mount float valves in the tank that are actually supposed to be RO shutoff valves, they are a couple bucks each. One valve per tank. The (mechanical) valve opens up to top off, and shuts off when the level gets back to the desired height. An electric float valve in each tank ($4-6 each) would serve as a back up. These would all be tied together in series through a solenoid, so that if one tank senses that the level is too high, the solenoid opens. On the normally closed contacts you run some sort of indication, be it visual (light) and/or audible (buzzer, could be annoying for others if you are not around). On the normally open contacts (which are closed when the solenoid is closed. System operating normally) you run the leads for a single solenoid valve that is on the main feed line to all of the tanks. You would have to set a second set of float switches up for the tank to run a pump to auto fill that.
If you are running this directly off of an RO system, you eliminate the need for the tank, pump, etc.
Trouble shooting could be a slight pain if you have a large number of tanks, but shouldn't be too bad. Manual checking of each valve would eliminate the most likely cause (sticking). Electrical would still be simple, just a little more time consuming.
Monthly (more frequently if needed) lift all the valves one by one to test for flow (mechanical float valves) and that it shuts the system down (electric float valves. Visual alarm is sufficient for general testing or each tank, then physically verify that the solenoid is shutting down the feed line).
I think this would have the most simple implementation and be fairly reliable and inexpensive. You could install a cheap switch to bypass the sensor for each tank (or manually install a jumper) to take a tank off line for maintenance or to take it out of service. The only issue that I see would be if you were away for an extended period. A failure of one of the mechanical valves that caused a high level for one tank, would shut down the ATO for all tanks.
Although with a single pump running all the time dead headed would be a higher risk of failing and taking the whole system down, unless it was a magnetically coupled pump.
If you set it up with a pump, you wouldn't need it to fill one tank at a time (with the individual solenoid method). Having each tank fill individually, one at a time, would be overly complex. The demand for the pump by any tank would start it up (pump switch on each solenoid wired in parallel), each tank would actuate individually to fill (its own solenoid would actuate), they would fill in parallel, just at a slower rate. The pump would shut down when there is no more demand to fill.
You could do each tank individually like you said, something in between that and what I suggested where tanks run in banks. You could run redundancy with pumps as well, where if the reserve tank level drops too low, a secondary pump kicks in to fill. You can get as complex and expensive as you want.
I'm assuming that if you are running enough tanks to warrant something like this, you have more than just a few (I'm pretty sure that I recall you are breeding shrimp) and are running a RO/DI system for top off (and making water to specific standards). If the RO system is a permanent install in the room, or in a spot where you could run a hardline, or PEX tubing, I'd go that route and run the ATO system directly off the RO system with one of those small pressurized supply tanks so your fill rate isn't limited to the immediate output capacity of the system (ie 100gpd = .07gpm).
The valves I was talking about are on Amazon. Float valve and water level sensor should yield plenty of results. Some are for RO, others for pools. You will greatly reduce your results by adding aquarium, but you may end up omitting some of the more desirable results. If you go with the in tank float valves, check the dimensions, some of them are rather large and obtrusive.
I usually feel kind of guilty using the quick reply... my replies are rarely quick.