I believe we used mostly 18/2 for speakers, 24/4 for motions (the little terminals can be tough to work with, so smaller gauge and possibly solid-core help) - and 24/2 for the contact sensors. Cat5 for the keypads of course. If you're going to run relay outputs that'll depend on what you're controlling - for me, all my relays are in the garage with the equipment they control, so that made it easy - a single Cat5 run to the garage with an 18/2 pair lets me control the sprinklers (10-zones), pool fill, garage doors, strobe - and leaves 2 free... and I can run a keypad out there if I want. In the cabinet I used leftover 18/2 for the power connections and bought 10ft of 18/4 from HomeDepot to make other interconnects as needed.