My buddy bought some used brass from Sportsman Warehouse and it was awful. I prepped it for him and I think I threw out 25% of what was there. The count was higher than advertised to compensate for bad brass.If you buy unfired brass it will most likely be SAAMI spec and you will not need a small base die or shoulder bumping. However bulk fired brass (especially military such as LC) may have been run through a machine gun that have looser chamber tolerances and allows more case expansion. I have an FN/FAL that was a full auto and it allows the brass to expand more than my AR-10 and I keep this brass separate.
I use a small base die for resizing because I have a lot of various headstand brass but you can avoid this is you buy unfired brass to start off with. As folks said above, there are different ways to achieve the same goal it depends on how much effort you want to put into it. Good luck and enjoy.