Nothing from the normal players as far as Prvi brass. Dig a little deeper. Brownells has Lapua brass but $88/100. Ouch.
I'm non as concerned with getting the maximum life out of the brass as I am with being able to shoot my Schmidt Rubin when imported ammo becomes more difficult to buy should another panic buy ensue as we near the election. Should I purchase a reforming die? Or trim the brass and size with my 7.5 Swiss full length sizing die and then fireform?In answer to the OP's three questions, they are all yes, yes,and yes.
Can anyone live with, work with, and or use a brass reformed/expanded diameter close to .020" larger at the base? How many full house loads do you want to run through the brass? How many times? I might hold the thought awhile yet. Just about any .473 rim would work, along with French and Swede. When things become unobtainium. maybe
.284 is made by winchester in limited runs. Best-o-Luck