Looking to LED mod my stick the hard way, what has changed in the last few years?

I have a custom stick with PS-14KN buttons that I built a few years ago. I always wanted to do some meme stuff with it, light up on press buttons etc, but hate the idea of buying those SMD custom disc LEDs for more than the cost of the button each. I just stumbled upon ridiculously cheap equipment from China, 100 white leds for $2, teensy knockoff boards for $2, terminal strips 10 for $2, absurd deals. Ideally what I want to do is find a bunch of small LEDs, glue them to the inside of my buttons, wire them up to a daughter board, connect that to my main board (Teensy 2.0) and get it all going, but it seems a lot has changed since I last was around here, so I have some questions for the old tech gurus.

1. What happened to toodles?
2. What type of LEDs fit within PS-14KNs? Going with 3mm 5v by default.
3. How do people control their LEDs nowadays? Is there a mainstream board?
4. Does anybody even attempt this anymore? I googled for a bit and could not find any guides that go into specifical details, almost all of them use the disk SMD LEDs or do it the hard way but don't show what they did.

Thanks!