The newest generation is the 9950X3D, with some advantages over the 7950X3D. I would not consider the 7950, unless you find it at a much lower price. Concerning the motherboard, those based on the B850 are a very reasonable compromise. The ASUS ROG STRIX B850-F GAMING WIFI (~290) would do well for almost anyone. If you want a high end motherboard with many more M2 slots and all bells and whistles, consider the ROG STRIX X870E-E GAMING WIFI (~450). Both support either the 7950X3D or the 9950X3D (may need BIOS upgrade).

had a 7950x non 3D upgraded to 9950x3D the 1st thing I noticed is not gaming but being 10-20°C lower despite using slighlty more watts in gaming (like 10w)
not only that but clearly the 9950x3D is incredibly smooth for gaming it's the smoothest I have ever seen
I had MSI tomawhak wifi on my 13900k intel before it burned (thanks intel for selling defective cpus) and am currently on a very expensive x670e meg ace (can't buy it anymore too bad it was the best AM5 motherboard) you can look at the MSI MAG X870E TOMAHAWK WIFI for 312chf on digitec it's a good perf/price
msi bios settings are complicated but they do update them regularly which is a good thing and MSI avoid the trap of asus, asus "says" it has x or y port but when you read the manual it says "if you use an nvme drive it disable 2 satas" or worse slows down your gpu pcie slot they also have really bad quality now I don't trust asus anymore and I had ROG for 10+ years

Just buy an imac M4. Any model will suit your needs.