Scare you off yet?
Reminds me of what a PITA a pool can be, glad I don't have one any more.
my liquidcrystal screen is limited in the amount of output. 16x2 is not a lot!
Simple, get a bigger one. Even better get a serial graphics LCD like the ones from 4D Systems, they have touch panels as well so you don't need buttons.
limited in the amount of input pins I have
Either move up to a Mega or use a MUX (like the 4051 or 4067) to get more inputs.
Rob