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)..
".. 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)
1984 Fast/Nicholson 345 "FastForward"