I can't help but wonder if it's gonna have original paint. If not, it could be either b/c or ss, no way to know until you get it. That color was ss well into the '80s.
That Ghobi biege is a pretty forgiving color (my mother had a 450SL in that color), and the factory paint is fairly soft. If it's in OK shape, I would rather use IP a few times rather than PG (and I'm not afraid to use aggressive stuff

). Be careful around edges because if it *is* original that paint has probably been through some abuse. But if it's in *really* nasty condition, go ahead and use the PG and be prepared to clean the cutting pad out numerous times as it gets loaded up.
Keep your polishing products off the plastic trim
I myself would probably switch to either Meguiars (those trade secret oils are great on ss) or 1Z (very user-friendly and seems to work well on ss) at some point and I'd wax it as opposed to using a sealant.
Just FWIW, if *I* were cleanig it up for resale, I'd do 1Z Ultra/cutting pad, 1z PP/polishing pad, Collinite 476S (so the wax lasts until it sells...wouldn't want to redo it after a month or so

). Meg's #26 would probably look nice on it, but I'd wonder about the durability.
If the 1z stuff is out of the question, consider using Meg's #80 (or even #9) after you get it into decent shape (and then top with the wax). Those trade secret oils will hide a multitude of sins and old ss really soaks 'em up.