Wiring a Custom Overhead Console

Hey all, been browsing the site for years, new poster. Sorry if this is the wrong section. I have a basic understanding of how 12v wiring works, but would like assistance. I am making a custom overhead console for my 89 F250 with the 7.3 diesel engine. I have the 3g alternator upgrade. On the OHC, I am planning on having a "master switch" that will provide power to the gauges and switches on it. Accessories that I have planned are: my coolant temp gauge, hour meter, manual glow plug switch, push button ignition, and 3 accessory switches (high idle, radio, and bumper fog lights). I also have a voltmeter/USB charger combo ( Amazon Link) that I would like to integrate. I have a 20 amp (2 prong) "fighter pilot" master switch, with a 20 amp push button ign switch. I currently have the push button ignition, manual glow plug switch, and high idle already wired with the switches located on the dash, but would like to relocate them to the OHC when I finish it I guess my main question is, do I need to wire in a relay or fuses, and where should I wire them in? Also, what gauge wire should I use to properly power everything? I have created a rough wiring diagram (just got off of a 72 hour shift and had a couple beers, sorry if it doesn't make sense). I guess if someone could take a look at the image I have posted and recommended where to add fuses, and/or a relay, or even if I've drawn this up right, I would greatly appreciate it. If someone knowledgeable in the subject could take the image and "draw in" fuses, and/or relays, (maybe even correct mistakes) that would help me immensely. Thanks! Daniel