I have a Precision 165 not sure how long I need for either but was just planning on measuring and adding 10 feet to each jib line side and 10 feet to the mainsheet. At under a dollar a foot I would rather over compensate and cut later.
-------------------------------------------------------------------------This page contains all the specs for running rigging from the manufacturer: http://www.precisionboatworks.com/parts/parts.php?boat=P-165.
Jibsheet is spec'd at 1/4" x 26' and mainsheet is 5/16" x 52'. You may want to increase the jibsheet to 5/16 to make it a bit more comfortable, but 3/8 will be a bit much. As far as length -- too long isn't quite as bad a too short, but underfoot it can be a PITA. Adding 10' is approaching doubling what the manufacturer indicates. Adding 5' gives you an additional 20% -- that should be plenty.
Trophy braid should be fine for your use and Defender's sale is a bargain.
Enjoy.