So, back to the point of this thread: the OP wants to buy some cars.
Aside from the obvious financial impact (which he says is not currently an issue, good for him!) for me the biggest issue has always been storage. But then I thought about it last night, and people that have serious money usually also have no problem building serious garage space, so I guess that's not an issue either. Me personally, I don't think cars should be stored, put on battery tenders and driven only occasionally just to keep things in shape, rather than being used and enjoyed on a near daily basis. But hey, people collect things, and so if your collection is more than one, than you do have to do some kind of juggling.
OK, that got us nowhere.
How about waiting a few years to see how things settle down? Then, if you still want a BW, find a nice used one owner garage queen and get that. The engine lottery is something that no one can predict, other than to suggest that more people than not have had zero issues.
As for the GR Supra, I just bought one of those (new) in December. It just turned 1000 miles yesterday. It's a fun car, I like it. The manual transmission shifter is much better than the typical BMW stuff, but the rest of the car, except for the body, is all BMW. So it feels all familiar to me, the only real downside is that it's a low production car and whereas you could take a Z4 to a BMW dealer with a pretty good chance of it getting repaired, anecdotal evidence is that when you go to Toyota for service, they are somewhat clueless. And, you know, Toyota. The land of Camry and Prius.
Like the BW, the Supra is difficult to find, difficult to purchase at a discount, and production is ending next year I believe.