Lofting specific curves from a list. Help :)

2 questions:

I'm having trouble wrapping my head around how I can identify specific curves from a list so I would be able to loft between them, not even sure if it's possible.  Basically, as shown in the join.jpg, I want to loft between the outside top curve on each of the shapes, ex, the two that i circled.  No idea how I would do this :/

Secondly, at the start of my definition I populate a surface with points, is there a way to use a image map to change affect the density of these points in different spots while still keeping it pretty random?

Thanks!