take a look at this for an idea of what you need. Substitute the sanwa buttons for similar buttons of the same size.

The Brook Zero Pi is cheap, supports the switch, and doesn't need soldering (make sure you get the version with the screw terminals).

you will need a crimping/stripper tool and quick disconnects .187 or 4.8mm and wire (if you have old ethernet cables you could use the 8 wires from that)

Good luck with your build and post it when you are done.

For crimpers, I mean something like this: https://smile.amazon.com/Klein-Tools-Ratcheting-Crimper-10-22/dp/B07WMB61J5/

It crimps in 2 places on the connector - and ratchets down to the exact right amount of pressure for the connector/wire size.

I wouldn't trust any crimp tool that crimps a single point or relies on my judgement for how far to crimp. ie. Nothing like this: https://smile.amazon.com/VISE-GRIP-Stripping-Cutter-8-Inch-2078309/dp/B000JNNWQ2

Crimping lugs onto battery cables (4 gauge and larger) I think that a single crimp point is fine, but that's an entirely different class of crimping tool/technique.

I think this is a great little project for someone just getting started. For most of my connections, I soldered the wires together. If you have never soldered before, it's not that hard to learn. Checkout a few youtube videos on how to get started. If you are not into soldering though, there are many other ways to connect wires. Wire nuts are very easy to work with, just twist the wires together and twist the nut onto the wires. There are also crimp connectors that allow you to push the wires into a plastic sleeve with a metal interior, and then using some pliers or a crimping tool, just squeeze the connector until it crushes down a bit holding both wires in place.

Also I should mention, to connect the wires you will need to expose some of the metal on the end of each wire. This is known as stripping the wire. A simple wire stripper like this makes the job easy. Or for a few bucks more, a self adjusting wire stripper like this makes it even easier.

For the parts that I linked, it should be very staightforward. The 12v socket comes with wires with spade connectors on the end. You can just push those right onto the posts of the socket. The batter holder I sent uses the same style clip as a 9 volt battery. You can just buy this harness to plug into the holder. Then all you need to do is connect the red wire from the pack to the red wire on the socket, and the same for the two black wires. Let me know if you need any more help at all. I am always glad to help someone learn a new skill, and so grateful to the many people that helped me learn along the way.

One final thought. Any electrical system you build needs to have a fuse. If things go wrong, and too much power is being used, the fuse will overheat, and shut down before a fire can start. For this project you would just need to add the fuse inline on the red wire. A 10 amp fuse with a holder like this should be fine.

wire stiripper/crimper and some quick disconnects.

you could probably use some pliers instead of a crimper.