Probably the best way to go. If you don't already own a .280 Rem and have a pile of brass on hand, why would you want to go through the fireforming process with it? If you need to buy brass anyhow, just buy the Nosler 280 AI brass and get to load development right off the bat.
As for fireforming, whether you use the Cream of Wheat method or simply load .280 Rem. brass with a mid to stiff powder charge of rifle powder and a .284 bullet, you're going to form that case to the new AI chamber dimensions which include a 40 deg. shoulder and minimum body taper. Buying the Nosler brass eliminates that step.