How to control points and join surfaces on GH

Hello guys. I’m very very new to Grasshopper and am struggling a lot with it, so I hope someone can help me, since i have a deadline soon to present this model…

Basically I am creating a candle shade, and I want smaller tubes to ‘come out’ of the bigger tube. I put random points on the bigger tube, yet when randomized, some tubes appear to be at the very top or bottom. so my question here is how to set a boundary, that for example, the smaller tubes should be no less than 4 cm from the edge of the top or the bottom?

And my other question is, how to connect the smaller tubes to the main surface?

I hope you understand what I explained and hope to get some answers, thank you!