+1 for Proxmox
I messed around for awhile trying to figure out the best way to make the transition from the Windows server I'd been using for a few years (latest in a line dating back to the original version of Windows Home Server) -- but like you, didn't want any downtime.
With Proxmox, and its excellent PCIe passthrough capabilities (recent motherboard designs only) the solution turned out to be pretty easy. I was able to passthrough the NVMe boot drive from my Windows server as a PCIe device, then I moved my big SATA drives over and passed those through as VirtIO devices. Amazingly, I was able to carry-on using the Stablebit Drive Pool software with all of its redundancy and folder duplication options across my data drives.
What's important about this story, is not so much the specifics of what software I was using previously, but that I was able move everything over to my new Proxmox platform unchanged, other than it was now virtualized. As a bonus this gave me a fallback position, as I could still boot natively with my original OS -- which in the early days of this setup was reassuring.
So, Id' recommend buying a motherboard that supports VT-d (or the AMD equivilant), and has two NVMe slots. Proxmox is at its best with at least one additional Ethernet port, and my motherboard has a 2.5Gbps port onboard, and I added a 10Gbps board for the CTs and VMs -- which I would highly recommend.