Well it’s a tricky question, depends on the budget and what do you work on.
As everything in the life it’s a trade-off.
First think you should take into account is what do you want to work on.
Audio?
Video?
graphs?
I would go for threadrippers (they have plenty of cores at a good quality/price) to take advantage of multiprocessing.
A nvme hard disk, at least SSD, no hdd.
Realise PCIe 4.0 is out.
The delicated thing is how many of everything.
1st thing how many gpus you can afford.
You will need a power supply of 400*n + 200 more or less.
If you are gonna work with video I would get .3090s and at least 64 Gb of RAM.
But in the end there are no rules carved in stone, depends on your budget, how many ppl will use it, research field…
Let me know extra details for extra help.