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.
"Our houses are protected by the good Lord and a gun
And you might meet 'em both if you show up here not welcome son"