Create and manage some kind of "ressources" for attaching/detaching parts from a ship.
Building strut or pipe will also need a ressource.

Interesting, could use metal and rocket parts. It would likely be difficult to code in really. I mean the game doesn't even give more mass to longer struts in the core default game. I don't know if there would be a way to make this part a bit more realistic. There is also the issue of needing to haul resources with you to do this, I suppose you could store a tiny amount in your backpack.

Adding onto this, you could always add a module to KAS that lets you produce any KAS part that can fit into a container and be carried around. It'll be a container of it's own and be able to produce parts using metal and rocket parts (and electricity, obviously).