I think you'll find it isn't that easy to keep switching out halyards. And, I doubt you'll notice that much of a performance difference unless you're putting up "racing" sails. So, one set of halyards should be all you need.
Sta-Set X doesn't have the "slick" feeling that Sta-Set (and T900) has. It'll tear your hands to shreds unless you wear gloves. For a halyard, it'll work fine and is an upgrade from Sta-Set. I have T900 halyards...unless you really need "low stretch" and/or you really like the "slick" feeling...a bit of an over-kill (even on a J/36).
As for sheets, regular Sta-Set is likely your best bet. The computer models probably say you could go as small as 3/8", but that's really too small for most people to easily grip. Size sheets so they fit your winches/gear as well as your hands.
Just my thoughts,
J/36 "Zero Tolerance"