Tom,

OK, I've added Umin and Umax sliders which should do what you want.

>> Do you have any background in programming / math ? <<
A programming background would be beneficial, but not necessary (I'm not a programmer).
As far as maths go, some high school level trigonometry is really all you need.

.>> Is there a thread collecting all the nodes available. <<
"Nodebundle for playing with nodes" thread charts the development of NE, but also my own skill acquisition. If you look at my early thread posts, the examples are very rudimentary and become more sophisticated painstakingly over time.
http://moi3d.com/forum/index.php?webtag=MOI&msg=7777.1

My best advice, if you want to learn NE, is to be persistent. Sometimes you find yourself at a dead-end, take a different tack, and just keep going.

Good luck
James
https://www.instagram.com/nodeology/