Best way to do a LCD menu system?

My project is a OBD2 car system which displays readings from the cars ECU to a HD44780 20x4 LCD display. I got some funding from a car forum for the project, I even have the PCB's being manufactured as I type this! So very exciting!!

On the 20x4 HD44780, I can display 8 readings at a time, so 2 per line with a line in the middle separating them. Now the thing is that there are going to be like 20 or more readings that can be displayed. I could easily have the buttons to cycle through the screens, but I need to be able to allow people to make their own custom menus.

I plan to use 3 push buttons, but allowed for 6 on the PCB (just in case). I guess one for move item up, another for move item down, and another to select item. Holding down the the select item button could enter an editor mode, then using the up/down buttons select an item to move up or down the list.

With using the EEPROM to store the locations, how could I come up with an item ordering system? I