Does this mod require the original mod to be installed?

No, feel free to install the original mod if you like, but this version does not require the original mod to be installed. In fact, you can have both installed!

How to get tubes to display something?

This is a two step process. First you'll have to connect your (most right) Nixie Tube with a combinator wire (red or green or both). The next step is to open the connected Nixie Tube and in the enable condition, select the signal to display the number of. Once the signal value changes, the display will be updated as well.

What does the update speed setting do?

It's the amount of Nixie Tubes that are updated every game tick. If you have huge amounts of Nixie Tubes, and you set the update speed too low, it might visually not update enough to have an accurate reading.

A higher value will result in more accurate readings and faster updating of all Nixie Tubes, but at the cost of more UPS usage. I usually leave it at 5, then I can account for more than enough Nixie Tubes to update. Setting it any lower won't impact it much (as you won't have a lot of Nixie Tubes), but you might have to set it higher if you go crazy with them (as in thousands of them). Usually I increase the number when I notice visually that they are lagging behind.