So the question I then have is, how hard would it be to virtualise my current Ubuntu server within Proxmox, both not having dealt with VMs before and having spent a lot of time on the server?

This is maybe less of a gift than you think and can also be learned with practice. It’s about having a growth mindset. If you practice framing things in terms of growing ability then everything becomes achievable and the challenge becomes enjoyable.

There’s only one quadrant of this that should be acceptable to anyone! Positive X, positive Y!