Computers are so fast these days you can have entire VMs in the background and not even notice them. Since Win10/11 come with HyperV and WSL you don’t need to buy any separate hardware to start playing with homelba/Linux stuff.

I doubt you would notice much a performance hit if any. What you’re losing out on is reliability. You playing games and downloading/executing stuff causes extra processes to run that normally wouldn’t on a server. The more processes running the more chances for a glitch in the matrix to crash the machine. You could also do an update that breaks compatibility with other programs (not so much an issue with Docker). The biggest point of a dedicated sever at home is the fact that you set it then don’t fuck with it - This leads to higher reliability.

Any computer can be a server and in most cases we ain’t pushing em very hard as we learn anyway

Depends entirely on your system specs and how many resources are dedicated to the VM’s. The VM’s you listed are very lightweight so would not be very noticeable unless you’re on an ancient processor or have an i3.

That being said, Docker is not very reliable on Windows so if that’s your host OS you may run into issues with VM uptime. Downtime of your daily driver will also cause outages of your VM’s. Gaming machines need constant video driver updates and are rebooted more often than dedicated servers, so plan ahead for that.

Depends on your gaming box.

If your gaming box has fewer cores (say, an older i5 or current i3 CPU), you might notice Nextcloud running. Pihole is so light I doubt you’d notice even if your gaming CPU was a potato.

If your gaming box is more than four cores, I doubt you’d ever notice.

I actually had a proxmox daily driver for the last couple years. I don’t play high-end games but it worked just fine with GPU pass through.

if you need a gui on the host I actually installed a desktop environment onto proxmox so i could use it as my management machine.

the really neat trick was a usb switch plugged into two different usb groups so i could toggle to the host (monitor connected to igpu) at will.

I cringe at the thought of putting pi hole on a gaming PC, you must live by yourself and have nobody else that relies on the internet. You shutting off your main gaming PC would shut down the internet for the whole household.

Most of my labbing happens between WSL and a few VMs in Hyper-V on my Win10 desktop.

The problem is, what you’re describing is not a lab. You’re describing a home server.