I would recommend saving the engine to an additional, seperate model file which can then be imported when making new models. Maybe do some extra folder called "library"
Concerning the rope: It could be done the way it is done for the current elevator (which I don't know.) I'd have some ideas how to approach this otherwise.

Models go into the resources repository. http://git.openclonk.org/openclonk-resources.git

> It's really important that the model works in the first place – later the uv-mapping and textures will follow!

Right! But also, before thinking about "seperating models", "bones" or "how does the rope work", I'd acutally like to see the real concepting phase through, first. That should include some color and texture paintovers, picking out a rotation to show the object ingame, putting it next to a colored wind generator prototype, trying out if that engine acutally fits on all the other buildings, stuff like that. sortof-kindof "Lets do /all/ the concept art first" before moving to the next stage. that way, changes in style and color won't affect models, uvs and textures as well, but only the concept art itself.