Top punches depend on bullet shape.
.45acp is usually sized .452
.45 Colt sizes can vary a bit more, I don't have one but expect either .452 or .454 depending on the pistol. Hope someone more knowledgeable can chip in on the .45 "long Colt".
I'd start with the .38 special myself, easy cartridge to reload (I'm told, don't have one yet) straight walled cartridge, headspaces on the rim, tons of reloading data. Does not use a lot of powder or lead.