Thanks a lot! To be honest, I didn't know there's a possibility to add multiple strokes to one shape and I still don't know, but I'd try to find that feature
Regarding a 3d lines effect, I hadn't a good example at the moment, but please take a look at: THIS ONE .
Parallel lines provide a simple 3D effect, but some designers use them also to add a depth into the project - making some elements bevel/embossed/engraved or creating another pattern inside. i tried to understand how they do that and I guess they make 2 different shapes, cut by the parallel lines of different stroke and then put the one on another. But maybe there's different way.