If you can not afford a real NIXIE tube watch, there is an alternative. It is this 4-digit 7-segment LED watch kit. It costs less than 10 euros and you can find it on most Chnese resellers websites. It comes as a kit and you will need to do a bit of soldering and assembling.
The most important advantages of ABS are impact resistance and toughness. Lego is made from ABS. It will also not deform in hot water, compared to PLA. On the downside ABS is hard to print. You need very hot printbed (around 110 degrees Celsius) and Kapton tape, so the first layer will stick properly. ABS can also warp and curl. There are also other issues in the Marlin firmware that need some attention.
The first step in electronics is understanding the concepts of current and voltage. There is a hydraulic analogy that helps to understand electricity, but here we will try to cover how it works on atomic and electron level.