Having tried azure local before (it seems magical but the more you use it the worst it gets, update failed for no apparent reason on only some supposedlyidentical nodes, the sdn was atrocious to deploy and was manageable from wac only), I would recommend proxmox over it anyday.
If you don't have linux expertise on hand and have traditional FC based storage, I would recommend something else, probably nutanix if your budget is big enough.
Why? Honest question, what leads to that Kind of size and why cant it use NAS shares or SAN disks for most of that data? Kudos on the migration!
When I get back to work I will finish the samba configuration of the ceph cluster front-ends to replace those elephants.
I’ve worked with a few major US grocers on very similar projects (some hardware only refreshes and one VMware to HyperV/Azure Local migration).