The most basic Mister system is a bare DE10-nano. Several cores will run just on this with no add-ons.
The first addition that may be required is an SDRAM board. I am not sure if this is mandatory for the QL core or not (I'm sure Marcel can answer this). Other than this you will definitely need a powered USB hub. You will need a Micro SD card and you will have to set it up to run the Mister system. This will allow you to run the QL core with a USB keyboard and mouse and an HDMI monitor.
You should get a heat sink for the DE10-nano.
After this it is a question of what you want to do with the Mister. If you want to use a VGA monitor you can either use what is known as Direct Video, which uses an HDMI to VGA converter to output original analog video via the HDMI port, or the IO board VGA port. I have never used Direct Video, but I have used the VGA port on the IO board, however I mainly use HDMI. There is info on Direct Video here: https://github.com/MiSTer-devel/Main_Mi ... rect-Video
The IO board is an addition that most people have. It has a conventional VGA connector, and also a mount for a fan (very much recommended). I also use it to output analogue audio, because I find that HDMI audio does not work with all cores with my monitor. It also has 3 pushbuttons for reset - core and system - and to call up the OSD menu, which is convenient, and a second SD card reader, which is actually required by very few cores.
There are other addons which can be useful - such as an audio-in port which allows loading games from cassettes in certain cores, but this is obviously not relevant to the QL. You can also get an integrated USB hub and other fun stuff...
Before you start, I think you need to answer a couple of questions, primarily 1) do you want to use VGA or HDMI, and 2) do you want to use any cores other than the QL?
There is lots of Mister information here: https://github.com/MiSTer-devel/Main_MiSTer/wiki
and here https://misterfpga.org/index.php
, and obviously on Youtube.