This is only supposed to be a jumping-off point. Trying to tackle this will take a lot more problem-solving.
Try plugging these components in and see what they do- best way for you to gain an understanding.
I had imagined you would take the resultant curves across the surface and pipe them.
There are many ways of doing the same things in GH, each with their own set of advantages/disadvantages. I have given you another way of achieving the same result which may hopefully be easier to understand and lead to fewer issues for you down the line.
Description of each component is in the image.
Here is the GH file; take a look through it, change sliders, recreate it… it will help your understanding.