collider types

Hi

Hopefully a quick one regarding collider components.

If I have quite a complex mesh, for instance a Star Destroyer from Star Wars, is it better performance wise to create a simplified mesh collider (which will still probably end up being quite complicated) or loads of primitive collider shapes as child objects created in the editor?

Also I havn’t worked out yet whether having collider components from the same gameobject hierarchy overlapping is a bad thing or it doesn’t matter? It seems to work fine collision wise but does it make a difference performance wise?

answered myself as this got lost in the abyss of crap stupid questions from people who can’t be bothered to read any of the manual or go through any of the video tutorials.