Wow, this is a very cool Jukebox-project! I love the light-effects. I think I will change my own Jukebox to something similar. Thanks for sharing yours!

220 - 470 Ohm.
Works best when the resistor is as close as possible to the panel (at the end of the line).

Thanks for your commend!
Yes, your version was my biggest inspiration! But I wanted it as simple as possible, so I used just one Button per player. And it becomes more difficult by speed up each round and the boost when you hit the ball as late as possible.

Now to your question:
I use the FastLED-Library. There is in theory no limit. The limit is the memory of the arduino. But when you use a processor with more memory for variables, you can use much more neopixel.
I found a discussion for this:
https://github.com/FastLED/FastLED/issues/288