I did something similar. I used Proxmox and then installed PfSense as a virtual machine. You might want to look into OPNsense and PfSense. There are addons for both that do the same as AdGuard and are free and open source. I had good experiences with pfBlocker

Either proxmox or esxi

As long as you have access to a a command line, you can install it manually. It’s worth noting though that I did a cursory internet search, and it seems like the developers are strongly against installing AGH on IPFire directly—so it would take some hackiness to even get it installed on IPFire directly. That said, IPFire supports VMs, so you could run AGH in a VM on IPFire.