nOxD,
Like you I am limited to 1 message a day still.
As others have said any Pi will work, 3B seems a good choice.
I have a few different ones and the 3B is what I think I will end up using.
The Pi OS is simple to get installed, especially if you are already conversant in Linux.
There is lots of great support and HowTos out there for the Pi.
As for talking to the Intelliflo Pump, there are other threads elsewhere, some have suggested that Arduino is easier and might be a better fit, but I like the idea of doing it all with the Pi. The rs485 is not native to the Pi, but the support for the different dongles (usb to 485) is good.
Personally I have not gotten mine connected yet, mostly due to time. It did not work right out of the box (neither Pi nor a windows terminal program) so I need some debug there. Might need to put a termination resistor on the 485, but that requires hooking up a scope to look at what is actually happening on the bus.
Do let me know if you get something working, seems like it should be straight forward, but life never is.
Thanks,
Doug.