First of all I don't have air or ever run air, just looking at your options and learning about air ride now.
5 port vs 7 port - Appears to just be a tank difference which I'd assume is just the amount of air flow you will be able to push through the controller. More ports=more flow.
So for the same price I'd say the 7 port, though it sounds like you would have to run more air lines. Though you can always block off the two ports and make a 7 port tank a 5 port tank if you wanted.
Also it looks like at least one port will be used for the auto tank drain fitting.