I am planning to make a mini NAS cum Pi Hole and Desktop Computer (For Emulation and Surfing) on my Raspberry Pi 4. I plan to install a desktop environment over Raspberry Pi OS, probably something like Ubuntu Mate. Is it a good idea to do so ? Is it like you add it to the Lite version or even the full version and it gives you a Raspberry Pi OS that looks like Ubuntu but runs like Raspberry Pi OS or does it mean it is going to change everything down to the core ?
This are many questions and they are mostly opinion based. If you install a Desktop from the default repository to a Raspberry OS Lite version you will nearly get Raspberry Pi OS with desktop. So just download and flash it to have a look at it, if it fits to your needs.