That's a huge list, thanks for the effort!
I have been to Lineapelle in Milan this spring and can only recommend it. Many different tanneries, components producers, distributors and also their own "trend area" where they showcase upcoming trends, it was well worth the effort going there and I met most of my leather suppliers through the contacts made there.
However tipps for all going to an exhibition: make appointments in advance, otherwise you will just be "walking around and looking to different booths", but not really getting the most out of it. I would really recommend planning the attendance beforehand, even as a visitor :-) Might be obvious for many people, but oftentimes you just go there to have a look and might be missing out on many opportunities!
Specific tipp for Milan: book your hotel/Airbnb early in advance, it is a very small city in terms of accommodation capacities and prices go up quickly to 300 Eur and more per night.