With Proxmox, you need less than 2 GiB for the base system without a swap partition, so 6 GiB should be more than fine to run a lot of things. Plus, you can always deploy a zswap, which is literally free RAM (albeit slower).
I have installed the full 16 GiB my Fujitsu thin client supports, but I've also installed a full-blown KDE with Chromium there, so I have the option to do configuration without a second PC. It's currently running an OpnSense that has 4.5 GiB allocated, and uses up to 10 GiB when running the config interface in Chromium, so there's still 6 GiB free plus a possible zswap extension.