IMO containerize everything. Containers save a lot of headaches, and time is valuable. You are correct that moving configurations is trivial with containers. Backing them up and restoring is also easy.
In the meantime you can install whatever you want in a VM - just keep track of the Docker configurations and move them when ready. I like Proxmox, but it may be overkill if you aren’t going to have a complex setup. The main selling point would be that you ‘containerize’ your OS as well, which means you can snapshot it and do various other tricks with running multiple OS’s. If your new server will eventually be a NAS, Proxmox can do other neat tricks like running TrueNAS/OpenMediaVault in a VM, or hosting a ZFS pool on Proxmox itself.
If you end up wanting to use Proxmox, you can also use Proxmox within a VM on your current machine to get comfortable in advance.