Bill,
Thank you for your input. Very Helpful.
I am thinking that 32 Relays, or x2 of the 16 channel relay boards, should cover the on and offs I need to accomplish.
If I can control those relay boards with an RPI3, and Still pump in my sensors, that seems more reasonable.
Hence why I am thinking an RPI3 paired up with a Mega.
That solves all my issues as far as connectivity, control, and reading sensor data.
I will have these connected to a somewhat large solar system, with some redundancy, so power should not be an issue.
My Solar Charge controllers all have a 5v 5Amp output on them that I intend to use to power the PI and relay boards. I'll power the sensors off of a separate 5v 5Amp supply.
I really need a single unit, as I am attempting to keep things to a single point of failure. Or as few as possible.
This would also allow me to use something like Unify Mesh Wireless on the farm, and connect the RPI3's up with a nice USB Wireless Card to Guarantee good connectivity.
Not only do i want to monitor my conditions throughout the year, but I also need the alerts.
With aquaponics, since the environment is artificial, a water flow failure or pump failure for example, can kill the entire crop within 2 hours. By allowing the pipe to run dry, the roots completely dry out as well.
So they are not very forgiving.
I need something that will allow me to step away from the farm, as this will be a primarily automated site, and be notified if things go wrong. So that i can drop everything and correct failures of the environment before they cost me a whole crop.
This will be mostly lettuce, so I only need certain variables.
But I am afraid of running out of pins in case I want to add sensors later on.
The RPI3 + Mega option seems to ensure that this wont happen.
As it should be capable of dozens of sensors per mega/RPI and cover my 32 relay switching as well.
It can also host the web page that all of this would report to.
It can be internal, and I would just VPN into it when I need to review information or see the dashboard.
Its starting to look like my all around solution.
It gives me the AVR and Python options, as well as others.
While seeming to meet the other requirements.
300$ - 600$ is still WAY less than the systems I am finding to monitor these variables that come pre-manufactured.
Its like 30,000$ for a monitoring and dosing system for a hydroponics greenhouse.
But with my setup that I am proposing, paired up with This:
https://robogardens.com/?page_id=943
Which is a simple assembly for testing water quality in a more detailed way.
These 2 in concert with a small surveillance system in each greenhouse, will allow me pretty good control and monitoring, for FAR less than places like Cropking.com are charging.
Plus I can do a full youtube and instructables series on it and show others how to get to a useful system more quickly.
Does that sound like an attainable goal as I have described above?