Space Frame issues

Good Day,

I am new to grasshopper and I am busy modeling a space frame that i intend to do an FEA on.

1. I have managed to create the 3D lines of the space frame but i need to select and isolate a few points on the lower grid to set them as supports for Karamba. (eg. on the four corners.)

2. I also want to be able to control the minimum distance between gridlines in the V direction.

your help is much appreciated!

I have attached the two files,

Thank You,

Matt