New Norco 4224 Threadripper build vs transplant seeking advice

My current unraid system is a little over a year old, it is a Prime B350 Plus from Asus, Ryzen 5 1600, and I have 12 drives including parity and cache, using a 2 and a 4 port sata cards.  There is also a video card which I am not really using but play around with sometimes in a VM.  It is 75TB, 97% full, and the hardware upgrade bug has bitten me, so I want to move to a Norco 4224 rackmount 24 bay chassis.  I think I might be able to get away with transplanting my current motherboard, but I think getting 24-26 drives connected problematic with the fact that it only has 1 x PCIe 3.0/2.0 x16 (x16 mode) and 1 x PCIe 2.0 x16 (max at x4 mode), and ideally, I would buy 2-3 used 8i SAS cards, or worst case, a 16i or 24i card.  I'm worried about PCIe lanes if I were to do that and keep a video card in the x16 mode slot, leaving only the x4, and a couple of x1 slots (which I think share the x4 slot lanes).  

This brought me to looking at alternate AMD boards with more PCIe lanes, and that means either a better AM4 motherboard, with 2 x8 slots and a x4 slot, or a threadripper system which is almost absolutely overkill but much cooler.  I feel like just replacing the Prime B350 Plus would be a waste unless I was able to sell it, where with a new CPU/Motherboard, I can then have another almost complete computer for selling to a work friend or doing something like pfsense.  Plus I'm not sure if having 2 x8 slots and a x4 slot is good enough. I have been building my own PC's for 15 years, but have never really had to think about PCIe lanes or SAS.  I have only ever had single graphics cards and have only used SATA cards if I had to.

To get an idea of what will be running, I have deluge, plex server, sonarr, radarr, and handbrake dockers running.  I want to try having a gaming VM which will connect to a 4K HDR display using something like a GTX-1080/2080/whatever AMD has next, slightly down the road.  It would be cool to have multiple gaming vm's with the additional ones being less powerful. I have though about putting pfsense on it in a VM, which I have never used, but I worry about network downtime and complaints from my family, also if I did, it would mean at least one PCIe dual+ port Intel NIC, which would need PCIe lanes.

The way I'm weighting is that a 24i card costs around $600, assuming I can use it in my current motherboard, and if I purchased a Asrock X399 Taichi and Threadripper 1920X, it's only $130ish more, plus about $50X2-3 for SAS cards, but gives me many more options and I could think about getting an NVMe drive or two.  I suggested selling my MB/CPU/RAM to a co-worker for $200 and he is considering it, plus I told my wife my intentions and she was okay with my $750-$1500 estimate.

I have also considered getting something used, like a SUPERMICRO 4U STORAGE SERVER 24-BAY X9DRI-LN4F+ from unixsurplus.com for $775.  So, I would greatly appreciate any advice.  Maybe my thinking is way off base.  I suppose any money I save could be spent on graphics/NVMe/storage.

Thank you.