My step-up from Pi was to ebay HP 800 G1 minis then G2’s. They are really well made, there’s full repair manuals available, and they are just a pleasure to swap bits in and out. I’ve heard good things about, and expect similar build quality from the 1 liter Lenovos.
I agree that RAM is a likely constraint rather than processor for self-hosting workloads. Particularly in my case as I’m on Proxmox and run all my docker containers in separate LXCs. I run 32GB in the G2’s which was a straightforward upgrade (they take laptop like memory). One some of them I’ve upgraded the SSDs, or if not, I’ve added M.2 NVME drives (that the G2’s have a slot for).