This article from newelementary may help you to understand the piece: http://www.newelementary.com/2017/03/lego-minecraft-2017-new-parts.html

Don't worry about this radius, I don't put them for this kind of part.
To figure out the other dimension, just make a grid with studs, see where the particular stud is landing and add a small gap on each side (like 0.3mm)

Just another one tip, I don't use n-gones. Mainly Quads and then tris. But it can be converted later 😃

Keep up the good work.

Edit: I just saw that there is actually a brand new article about this part on newelementary.com

Thanks for the links. I saw them but never get deeper in the reading.

I noticed for n-gons. I already use tris, so it won't change any things 😉

Excellent idea for the grid. I'll test the part with that. Thanks 👍