My opinion is based on DAZ3D rendering or at least, the basics I've picked up here on the forums over the last few years.
CUDA cores are the workhorse of a graphics card (GPU). The more CUDA cores, the more simultaneous things a graphics card can juggle. It's not a singular "more is better", but generally the more CUDA cores in a card - the more effort has been put into the supporting hardware on the card too.
The other aspect of graphics cards is the amount of RAM (VRAM) on the card. The more VRAM, the more surfaces/objects can be included within a scene before the render engine has to abandon using the graphics card (VERY QUICK) and instead fall back to using the computer own central processor (REALLY SLOW).
You can buy more than 1 graphics card per computer, but it will generally only affect rendering speed. Having 2x cards with 8GB of VRAM is not 16GB of VRAM - it's still only 8GB, just rendered faster. So if you want large scenes, then pick cards with the maximum VRAM you are willing to pay for.
Beyond that, personally I would aim for an Intel i9 processor (CPU) - again, find an i9 and just pick the more expensive you care to pay for. Then find a motherboard that works with that flavor of CPU. Alternatively, AMD's Threadrippers offer a lot of CPU cores per processor for a very smooth experience.
The choice of motherboard will determine what type of memory to aim for. Again, if budget isn't an obstacle - just buy highest price per 1GB. I'd regard 32GB of memory pretty much a minimum for a high end PC, though you could go for 64GB or even 128GB. Honestly, anything above 40GB is probably overkill for anything except video editing. I'd go for 64, but I can see the appeal of 128.
Given that rendering is all about the graphics card, my opinion is that the speed of the hard disk (SSD or NVMe M.2) probably doesn't matter overall. Sure, loading the textures and models fractions of a second quicker is always nice, but when a render might take hours... that speed is kinda wasted. I'd still buy an NVMe drive for my boot/operating system disk, probably a second one for my "work-in-progress"/documents disk and then a large SSD for my dumping ground of "everything else". Which means your motherboard needs to either take 2x NVMe drives onboard (1 is more common) or a PCIExpress card to hold that 2nd NVMe drive (or just forget that 2nd one as an extravagance and get 2x SSDs).
You could also consider a RAID array too (3+ hard disks clustered together to either work faster or offer disk protection if one hard disk crashes). There are also external RAID arrays called NAS (Network Attached Storage) - they're great, since the hardware only needs to do one job. A great alternative to my "dumping ground" internal hard disk.
Minimum 1500 Watt power supply for something with lots of graphics cards and a big central processor. Higher if you decide to go for 3+ graphics cards.
Most motherboards will cope just fine with 2x graphics cards... more than that, you need to ensuring the board has enough expansion slots. Just keep in mind that if you aren't using water cooled graphics card - 2 cards right next to each other is a lot of heat in a very small space - especially if one card blocks the fans of the other. Larger motherboards will sometimes have enough slots to leave a sizeable gap for air cooled GPUs.
Finally, consider giving all these requirements to a professional PC builder and have them build the system with a full water cooling system too. The whole thing will be quieter and will prolong the life of the graphics cards by keeping their operating temperature much lower... or shorten their life significantly if the water leaks.
Forget laptops. I mean in general, not just rendering.
