This would be my first keyboard build of any kind, so I want to make absolutely sure of what I'm getting into. Prices aside, the parts list is:
-GH36 PCB (which I intend to cut down to 4x6)
-Teensy 2.0 microcontroller + metalliqaz's keymap thing
-Switches (24 for my build)
-Keycaps that fit the switches (1 per switch (duh))
All sounds good. If you're cutting it down to 4x6, you could get away with a cheaper controller, but teensy 2.0 will definitely be easiest if you don't want to mess with firmware.
-Diodes (1 per switch? ... what type?)
Yes, 1 per switch. I use 1N4148:
http://www.ebay.ca/itm/New-100-Pcs-x-1N4148-Switching-Signal-Diode-SALE-/151347253015-LED + surface mount resistor (1 per switch IF you want backlighting, resistance value depends on LED and assumes there's 5v on the line)
Yes to the LEDs. Resistors should also be through-hole, as of the last time schematics were posted (admittedly, that was a while ago).
-Transistor (... also only if you want backlighting? Just one? What type?)
Yes, the transistor is only for backlighting. Its purpose is to allow the LEDs to tap VCC directly from the USB input to the teensy, while still being controlled by one of the teensy's I/O pins.
I used a 31 cent transistor, Mouser P/N 512-MPSA29, which should handle up to 40 20mA LEDs.
-Usb microB-to-A cable
Teensy 2.0 has mini-B, not micro.
-Case (will most likely have to hand-make it)
There's a couple of case designs in this thread, but I think they're all for the full 6x6, so hand-making one is probably a good option.
-Plating (Is this needed? What exactly is it for, just for plate-mounting switches?)
Plate is optional if you're using PCB-mounted switches, which I highly recommend you do. If you want to use a plate, that's something you should consider when working on a case.
Finally, what do I need to cut the PCB? Pliers? A tiny jigsaw? Should I sand it down?
Just a hacksaw should work, although there may be something better. Several options are given on stack exchange:
http://electronics.stackexchange.com/questions/1151/how-do-you-cut-pcb. Make sure you take proper precautions when cutting to protect yourself and your health.
Please excuse my terribly noob questions, I really am interested in this board.
Not at all, we all have to start somewhere!
I can't think of anything else off the top of my head that would be needed -- and really, even a case is optional, a couple of the prototypes were built just with some bumpers on the back of the PCB, and placed directly on a desk. Functional, if not the most aesthetically pleasing.