Working as a lead based paint renovator, I use Festool everything except for the hose.
Bosch makes this one available on Amazon that's about $80 cheaper and 5' longer than the Festool hose and fits Festool connectors perfectly, though is not antistatic.
For quick material removal, I use my RAS 115.
Follow that up with my RO 125, first in grinder mode and then in orbital mode.
For corners or polishing, I like my RO 90, which has an interchangeable delta head, (triangle shaped), to sand corners and tight spaces.
Look for Surfprep pads when sanding contours, as they can be fit to Festools.
To the OP, if you were to just get 1, the Festool RO 90 would be my choice, since you can put it in grinder mode with heavier grit to quickly remove material, then switch to orbital mode to use as a finishing sander, and as mentioned, it comes with an interchangeable delta head, and it's also a very effective polisher.
Side Note, nobody in the history of civilization has every just had one Festool sander though. They are the lays potato chips of the sanding world in that you can't have just one.