The CX750 isn’t a bad PSU, but not the best. It’s an idea to eventually change it, but it’s not a big priority.
You say you’re baking, so large quantities of ram is a must. I’d suggest 32gb is a good start point. Also, a cpu with good multithread performance will help speed things up a bit. But if you need to budget, consider a processor with a good balance of single and multithread performance. Not the cheapest budget cpu, because you’ll soon find yourself wanting to replace it. And not the biggest, baddest 64 core cpu because you don’t have that budget. A balance of high clock speeds and core count will do wonders.
Look at benchmarks and prices. Notice I’m not recommending a specific processor or brand. That’s something you need to decide through thorough research.
And don’t try to go “future-proofing.” Always expect you’re going to upgrade again at some point especially if you’re budgeting.
As for GPUs, high poly obviously needs high vram. An RTX 2070 with 8gb should suffice for some good sized scenes.
The board should be a place you emphasize a little more than others. You want a good quality board with good expandability. Not future-proofing per-say, but just leaving a little room for inevitable upgrades as you see fit. And cheapo boards, well let’s just say some cheap boards aren’t going to take the stresses of rendering over a long, continuous period of time.
And cooling, can’t stress this enough. Pushing high poly complex scenes is going to generate a lot of heat over a whole lot of time. Don’t skimp there.
So in general, think of how your hardware handles your scenes.Then look at the hardware you’re considering, and think of how much it would improve. Plan it all out and look for sales. A good idea is incrementally upgrading, and not a massive overnight upgrade. Maybe get a new board and processor, but keep your existing gpu. If you’ve got compatible DDR4 ram, maybe carry that over and add a little more. It’ll allow you to save more money to buy better hardware a few months from now as costs go down.
Me, I’m still cooking with two e5-2697V2s, 64GB ram, a titan x, and a GPU carrier with 4 mxm cards. It’s old, but does its job quickly and cheaply and is comparable to some render srvices. Aside from drawing over a kilowatt and a half.