I prepped the build for a 4090 by including a PSU that includes the new 12-pin power connector standard. That 3090Ti also uses it. And the PSU still offers 4x standard 8-pin PCIe connectors for something like an AMD 7900XTX which will be the other new card launching soon.
For gaming, the 13900K only offers a very small increase. Really you could go down to the 13600k and still have 95% the performance, but the 13700K is a nice compromise with its extra two P cores. Essentially a 12900K with a little more cache and frequency.
Again, for gaming, there really aren't any games that demand that much memory. If you like to highly multitask and run a lot of background programs, maybe. 2x32GB would be recommended then. Getting high speed memory to work with 4 sticks has proven problematic.