OK, I'll take a stab at it!
line: you might consider going to 10 mm spectra core
line here. Easily strong enough, and with the smaller diameter, you would not need to remove the core at all (something that I do not like because of UV damage to the remaining cover, weakening the part which gets the highest loads).
For the sheets, 5/8 double braid dacron would be quite adeqate. I have moved to using eye splices at the ends with separate soft shackles to make the attachments at the clew. Works really well, with little hangup and easy removal
when needed. I also changed from 5/8 down to 14 mm (9/16 in Yank speak) with good results, but my boat
is lighter and has a smaller genoa
than yours likely does, so the smaller line might be too stretchy.
Good luck with the decisions,