Sorry, I have no idea how to setup a decent system. I would ask here:
I use a 2950x, it’s a medium speed CPU, but good enough to feed the GPUs. I use one 1080ti for display and two 2080ti for rendering. I’m happy about the render speed. On my wishlist for the next year is a 3090 since it could double the speed (I’m not sure, we will see.)
I tested NVlink one year before but I got no possible scene size increase. If a scene of 8 complex blocks needs 11GB than it crashed with 10 blocks also in NVlink mode. Since one card is place outside my machine I can’t quick add the NVlink anymore. OK, I could place all cards in my machine, but than there is to much heat on the long run.
I’m a little bit lazy to test it again since NVlink cost some speed too and at the moment 11GB are enough for all my scenes. The 3090 (24GB) could allow me to render more complex scenes, but without the 2080ti. I think, this will be ok. So I could render 95% of my scenes per 2x2080ti+3090 and 5% of my scenes per 3090 only.
I wouldn’t spend any thoughts about how low the RAM setup could be. It makes so much more fun not to think about RAM so that I use 64GB. So, I can work on a complex scene, open a second complex scene without to close the first one, if an other client needs a quick render and don’t need to be angry about the long time to close/open the first scene. Also in this time can let Photoshop open, where I adjust a high res image. In the past 32GB wasn’t enough for me. I needed to close programms often.
Some times, for medium scenes, I use my display card 1080ti additional to the 2080ti, but some times, if to much memory is used and the display card crash, it can cause that a restart of the computer is needed. Best, don’t use the display card for rendering and the system is more stable.
Maybe the current discussion here could be interesting for you:
How much money you think to spend for your system?