Here's a tip... the winchers don't work well on sheet winches.... You'd be better served to invest in a set of "cam" cleats on risers to keep the sheet level. The you just snap them in and out (no fairleads on the cleats) Using the winchers on sheet winches will inhibit your tacking speed and not allow you to grind in the sheet one handed like a regular self tailing winch... you still have to strip the line off by hand... the winch has to be fully loaded to operate which is unnecessary except in hard conditions.
The 3/8 line will be fine... you'll get used to it quickly, and you can always wear gloves . You can go with 7/16 next time if you want, but 1/'2" is pretty beefy for a 30 ft boat.... totally unnecessary for the increased cost.