If anyone's interested in working together, email is in my sig.
An Arduino would be more than capable of running this logic, and an Ethernet one would even be able to log to the website the same as this setup does. However it's been really helpful being able to SSH onto the Pi, and tweak the code around in the environment where it has access to all the inputs. Especially considering that I live over 100 miles away from the installation!
Speaking of which, I might just hop on and run the pump for a bit, why? Just because :)
Surprisingly, a lot of things don't require an OS. Lack of networking is the biggest drawback, IMO.