As far as video editing goes, the Mac mini should be fine. It's been a while since I used 3D rendering software; I'm not sure how much they can draw on the graphics card now, or if they're still more CPU-reliant. I have no experience with AutoCAD and can't remark on that, either.
One problem you might run into with the Mac mini is with Bootcamp. Based on what I've read, the eGPU can be a bit finicky and it might require some tweaking to get it more stabilized. Others can chime in with their experiences, but if you're going to be using Bootcamp heavily, the Mac Pro options might be better.
The Mac Pro "can" seems like the worst option to me. It is the least expandable at this time.
The standard Mac Pro tower can still be upgraded to be a more current system, but that depends on how much you like to tinker. I'm not sure how the processor compares with more modern processors; looking on Geekbench, Mac Pros with the Xeon you mentioned have as single core score of around 3,000 and a multi-core score of around 27,500. The Intel I7 in the Mac mini 2018 has single core scores around 5,000 with multi-core scores around 22,000. Most of your applications will be able to use multiple cores, so the Mac Pro tower should still offer you good and potentially better performance than the Mac mini. The only potential snag here is that the Mac mini has Apple's T2 chip, which handles some video encoding tasks and reportedly does so faster than the processor.
Crunching the numbers, then, the Mac Tower might be the best for performance and expandability... but I'm with you on feeling a bit nervous about spending that amount on a computer that is now seven years old.