LVM is just a way more flexible partition table. It gives you the possibility to grow partitions at a later date. You probably not think you can do that with MBR or GPT too. Well yes, but only when the spare room is adjacent to the partition you want to grow. With LVM you can grow partitions even if the free space is somewhere else on the disk.
So you can grow any disk ‘partition’ at any time as long as you have some free space in the group.
Another advantage is that you can encrypt logical volumes easily. Usually that’s supported when you install the OS.
You can also stack LVM on top of a software RAID, so you can create a mdadm from a disk partition of several disks and create a VG on that with LVs to spilt it into pieces.
I usually use LVM on every server. There is no need not to and gives you options for the future.
Install the proxmox iso directly on the hardware. Then setup a Debian without DE in a vm to run docker. Use Portainer to manage Docker containers.
Storage can then be assigned via Proxmox to the vm’s that need it.