[Question] What should I look for in a mini PC to upgrade

Howdy All! I've been self hosting some services on a pi 4 for a year or two now and have been fiddling with new services lately. I realized I'm pushing 60% or so of RAM and maxing out the SWAP file while fiddling with things. I currently just set up a nightly reboot as a temporary solution but I'm thinking about picking up a mini PC of some sort to replace it with, and wanted to get input from the community (Read: people smarter than me haha.)

I'm happy to hear any preferences anyone would care to share on hardware. I know obviously more RAM is key, as far as I'm aware CPU isn't super important and any recent-ish box will probably have a fine enough processor in it, and of course I'll probably end up getting a bigger external drive to hook up to it but that's not a big deal.

Also, I'm currently running docker/portainer on an OMV core, just how I learned/got into self hosting. Should I take the opportunity to learn Kubernetes or some other big boy system? I've not done alot of reading into it but I know clusters are gaining steam these days even for self hosting, would that be valuable to learn more about as a hobbyist/enthusiast/whatever? I'm fairly competent and used to have some CompTIA certs but as such I know better than to unnecessarily complicate my life lol. It sounds cool but I don't see a use case in my personal usage.

Thank y'all for your time and knowledge!

I'm currently running: Baikal, Bookstack, Bitwarden, Duplicati, Filebrowser, freshrss , Linkwarden, Apache, Navidrome, nginx, portainer, rpi-monitor, searxng, stirlingpdf, syncthing, watchtower,

I'm considering: Nextcloud, Maybe a game server or two depending on the needs?, Whatever else seems interesting, I guess :P