Threadripper is the only way to get more than the standard 20 PCIe lanes (and really only 16 lanes to the slots, on all but one board). It's possible that OP would have gone with a lower core count version if one existed, but the minimum buy-in on Threadripper 3000 series is the 24 core model.

tbh this is kind of one of the ideal use-cases for Epyc. And with the way AMD has set up their pricing, it's actually no longer cheaper to use the workstation processors, in some situations it's significantly more expensive, they are really ripping you for the clock speed, and removing a bunch of other features in the process (RDIMM/LRDIMM support, etc). I strongly encourage everyone doing homelab and home ML rigs and similar stuff to really think about whether they want Threadripper, bearing in mind that threadripper is often more expensive than Epyc. It's no longer an obvious choice that server processors are for servers and home users can only afford workstation, it is the other way around.

AMD offers some low-core-count single-socket Epycs that are ideal for "lighting up the platform" tasks like this. Like, 7232P is a $450 processor and the 7402P is $1150. And they don't offer anything like that on Threadripper. They clock slower, sure, but they're not really using the CPU anyway. And that gets you a full 128 PCIe lanes, octochannel memory and RDIMM/LRDIMM support so they can stack in the memory.

If they want to game on it in their spare time then sure, Threadripper is probably the way to go.