For your setup, I would stay with a Dacron main, 2 partial + 2 full battens to maxmize shaping with minimal flogging. Definately a loose foot on the main if you plan to use the outhaul - you might want to consider a shelf foot (extra material at the foot), but I have no direct experience here. Try to maximize the roach to get some more drive on the light air days, especially off the wind where the genoa might be in the wind shadow of the main. A 7-8oz material weight should be appropriate for the main. Your choice of reefs - I have 2 reef points on the sail, but I only have one permanently rigged. I figure if I need 2 reefs in the main, I should probably be motoring.
For the genoa, from which the C27 derives much of its drive, a 140-145-150% is probably necesary for the light air conditions you describe. Go with the 140 if you can increase the mainsail area - it will furl down to 110 and keep good shape. Otherwise, the 150 is the better choice, but realize you'll still have a bunch of sail area up even when reefed. A rope or foam luff is mandatory to keep good shape when roller furling down in higher wind. You might consider upgrading the sail material to a premium Dacron, like North's softer Norlam - maybe 7oz. UV protection for the leech and foot is a no-brainer if you are keep the sail hoisted on the roller furler.
Keep us up to speed on what you decide.