Yeah, you’ll need the whole control system. WAY back when you’d have been correct, but since the RIO (c, then Robo) has been the control system you get one as a rookie and then have to buy more if you want them.
If I were you, I’d focus on the PDP and VRM for right now. If you’ve done proper labeling, the RIO will be easier to swap in and out than those. If you have pneumatics on both robots, you’ll need the PCM as well; otherwise ignore it.
For next year: Use FIRST Choice and prioritize the RIO and PDP.
(Personal note: I’m eyeballing the Gorgon myself, for an offseason old-robot rebuild. Old is an understatement.)