There might be a way to offload services inside StartOs but i didn’t see it.

You can configure an external drive to store your VMs in Proxmox if you do not have the space for one more internal drive.

You can also do what i’ve done, rip out and clone the internal drive to a bigger one. You’ll have to extend the partition and volumes to be able to use the extra space. I can point you to a guide if you want to do that.