Lenovo T-series is generally a good pick whenever you want to run Linux.

I’d say the same for their USFF and SFF form factors as well. Great systems for homelabs, I have several (and my laptop is a T495, and my son has my old T470s).

Problem with laptops and (u)SFFs is storage capability. If you want a NAS you need some sort of external JBOD or you will be limited to 1-2 storage disks (and possibly have to boot I.e. truenas from USB).

If you can find them with a PCIe slot (or extra m.2 slot that exposes 4 lanes at least), you should be able to get a RAID card and rig up a way to use eSATA and some sort of external disk enclosure though.

Pay attention to performance/watt. Consider different boxes for different roles if you want…I.e. ZFS doesn’t need a lot of processing power, but it does like RAM. If you have a system that can use dirt-cheap DDR3(L) like a 6th or 7th gen Intel, that may be a better choice for NAS-only.

Then use a more powerful NUC or (u)sff for proxmox and run LXCs or VMs on it.