With them so cheap on eBay, I’m considering getting a Mac Pro 2013 to replace my 2014 iMac 5k. I’d like to pair it with the LG 34BK95U-W which is a thunderbolt 3 display. Is this even possible with dongles or two ports?
I’d say firstly don’t bother getting the Quadcore Mac Pro. I have the 4ghz 5k 2014 iMac and my Mac Pro came as a Quadcore and benchmarked lower than the iMac in Geekbench and the D300 GPU’s are not amazing either. I upgraded the CPU to a Sixcore and now it does beat the iMac but not by much... so unless it’s one of the higher end 2013 MP’s I wouldn’t bother tbh
The online info is a bit vague but although it should work with either a TB2-to-TB3 adapter, MiniDisplayPort to full-displayPort adapter or HDMI cable, I don't think you'll get the full 5k resolution without DisplayPort 1.4 support and/or 'proper' Thunderbolt 3 (it's not even clear that you'll get 5k without last-year's model mac with the newer TB3 controllers that support DP 1.4).
A cheap/used 8/12-core Mac Pro trashcan is an interesting prospect but you might have to forego bleeding edge display technology and maybe look at a pair of 'only' 4k displays to get that real estate...