Re: 30/338 ammo
7RM = 7mm Remington Magnum.
Same basic case as the 338 Win Mag just different bullet diameter.
Cases for the 30-338 Win Mag can indeed be made from a 7 Rem Mag case. Advantages would be a smaller change in neck diameter in necking up vs necking down. Also for me, locally, 7RM brass is more plentiful and cheaper. I've yet to shoot any 338 brass in my 30-338.
Also, a two die set is fine. A three die set gives the option of neck sizing only if desired.
Reloading really isn't complicated, but certainly does require attention to details.