It all depends on how accurate you want to be?
For my AR-15 I need to full length re-size each piece.
For my Bolt .223 all I need to do is neck size.
This causes a problem. If you neck size and bump the shoulder the brass lasts longer. Some say it's more accurate. Look to the Benchrest shooters and they all full length re-size, that should tell you something about accuracy.
Should you mix these two up bad things happen. The case gets stuck in the AR-15 that only fits the Bolt gun. You extract the case with force and dump the powder into the AR-15 action. Everyone has done it. In a dogtown 1 mile from the rig and no access to the cleaning rod you walk.
I just this year started Full length re-sizeing all .223 ammo that I use and have been very happy. It is a no brainer, never a worry about "will it fit". The length of the ammo in an AR-15 is also very precise, if it's over 2.260 it won't fit the magazines and needs to be singe loaded.
For a volume shooter, you need a progressive press. I still use a single stage press and do 100+ each night during the shooting season with ease. The powder dictates your success, the long grained powders don't measure very well in a progressive press and smaller grained powders are usually chosen (ball) small extruded ones.
So if it were me I would start with a single stage press you already have and learn the ropes and add all the bells and whistles (progressive) later.
"Happiness is knowing the Barred Owl is Eating the Spotted Owl and environmentalists are watching Nature take it's course"