Yeah na, put your home services in Tailscale, and for your VPS services set up the firewall for HTTP, HTTPS and SSH only, no root login, use keys, and run fail2ban to make hacking your SSH expensive. You’re a much smaller target than you think - really it’s just bots knocking on your door and they don’t have a profit motive for a DDOS.
From your description, I’d have the website on a VPS, and Immich at home behind TailScale. Job’s a goodun.
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).