The other factor to consider is to make sure the software you're planning to use will actually utilise all those cores and threads. Look for real world examples.
Also if you're planning to be doing a lot of rendering, consider building a separate rendering machine - so your main PC is still fully usable while it's running. You can also look at more specific graphics cards for rendering rather than the gaming style cards.
The software I use does prefer more cores and threads.
You make a great point about building a separate machine for rendering...something I hadn't considered.