Hi there!
TLDR: I want to design an aquaponics controller which is better/cheaper than the ones that I found online. I came here for some advice from the pros.

I was looking around and found no aquaponics controllers which know the following:
- Cheap (<200$)
- Can measure the power draw of the motors, and thus enabling redundant pumps ( basically you turn on the second motor if the first fails ).
- Can measure multiple ( > 10 ) water lever sensors which use AC not DC current to sense the levels, so they wouldn't degrade water quality.
- Can measure ph and water temperature.
- Connets to a wifi and has a nice interface from the web. Possibly connects to cloud so it can be monitored from far away, this can be fairly complex because of security.
- Is open source: all of the scematics and software are available with a good license, and made with open source software.
- It can control up to 8 power plugs with solid state relays ( 4 lamps, 2-2 air and water pumps for redundancy )
- It has a small touch screen display, so one doesn't have to deal with wifi if something goes wrong.
- Is user friendly enough to be used by a total noob so you won't have to program firmwares etc.. just to get it working. You just plug in the things, set it up and it works. Bringing down the level which needed to use such a system is important for me.

I think I have to experience to pull this off, having an electrical engineering degree + node/React/AWS(cloud) experience for web interface.

1., From what I've heard water pumps occasionally die which cause the death of the fish in the aquarium. By measuring power and water levels the system could see if a motor fails and switch to other one. I haven't seen this in any system, why?
2., Is water conductivity measurements important in an aquaponics system? If so then I'd also add that to the pcb.
3., Is adding more water, managing ph and buffers autamatically important / should I automate these things too?
4., This pcb would include high voltage parts too ( the relays for switching motors ), but I would isolate them ofc. Is this something I should be worried about?
5., Should I add an output for a fish feeder?

I plan to make the prototype with a beagleBone black / raspberry Pi and then move to ESP32 since it would get down the costs by a huge margin.

My plan is to make a very very modest living out of this. I live in Eastern EU so I don't have high standards, but I have many ideas for sustainable agriculture / automation, and I would love to devote all my time to this. Of course the PCB would be open, but I plan to sell it if someone wants to support me when it is ready. Do you have a recommendation for a sales channel which would work with this community? Should I sell it on my own site?
I would also charge for the fully cloud option ( which I would have to pay for to be usable ) is this a good idea?
I progressed a lot already with the schematics but I would welcome any guidance / tips / needs!