[Lain]

First update:

I decided that I don't want to do too much soldering if I'm just prototyping and it's the middle of Winter in Canada. Don't want to freeze to death if something breaks and I need to resolder, so I decided to freeze to death today to save it for later.

I soldered the (broken/brute-forced) USB header to some wires, and soldered some headers to the back of the Teensy which contains the VCC, GND, and two digital pins so that I could prototype with a breadboard.

Schematic (Fritzing):


Image:


And then I plugged in a microUSB STM32 NUCLEO32 F303 device to test if it was soldered correctly. I connected the data pins to nothing and just wired up VCC and GND to the Teensy, to ensure that the Teensy alone was powering the device:


Success!

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While researching a bit more, I found one kinda big tradeoff for using the Teensy 2.0 which was changed in 3.6(++) and the new Teensy 4 (which I want to get my hands on, it's 600MHz and full 32bit! Embedded Linux NOW!)
It can only use 3.3V power. If you feed it 5V or more, it'll fry the chip.
Negligible for out use-case, probably, but if you plug it into a keyboard that needs 5V (think: fancy gaming keyboards with all the lightning and features) then it'll probably kill the device.
But, in an office setting, most keyboards are pretty basic so there will be no issues there.