Re: Mainsail Design Question...
I think it's a "yes" to most of your questions... Much of the extra cost would be in labour for sewn triradials. If this is not just a hypothetical I'd suggest that crosscut is what you want for your boat.. Likely not realize the performance benefit of triradials (jmo)..
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)