The details come with the Blender Advanced plugin. It costs $25. Here's a breakdown of what you get for free (Lite) vs $25 (Advanced):

If you are using the Blender plugins, there are tick box options when you import your zmbx for real geometry... for the LIte version you can toggle the Stud logos on or off here. But most of the details you described come in as bump maps which fake the extra geometry by using materials. If you export to any type other than zmbx, you choose if you want stud logos at the time of export.

As far as making your own pieces...

1. Custom decorations are possible in Mecabricks. Here's a tutorial: [url]https://www.mecabricks.com/en/forum/topic/2925[/url]. If you need the part in Blender, then you don't have to upload it to Mecabricks... it's possible to just do the decorations in Blender, but I would start with an already decorated part to get all of the nodes you need for the material.

2. Adding custom or new parts (different mold/geometry) is not possible in Mecabricks. At one point it was. Somewhere on here Scrubs has a thread for how to submit a new part, but it is outdated. If you need a custom part for Blender, you can model it or possibly pull it from another Lego CAD program.

Cheers!