Proxmox is an environment for virtual machines and containers.
SSH into Proxmox.
Enlarge a disk by using:
qm resize <vmid> <vm-disk-to-enlarge> <size>
For example:
qm resize 100 ide0 +100G
After that grow the filesystem as described in the disk-management article.
To use GPUs or other PCI devices you need to work with PCI passthrough. For documentation you can look in the Proxmox wiki. There is also an article on reddit, that focusses especially on windows 10 VMs with GPU passthrough.