Hi there,
This is Bogdan from Romania.
I'm a mechanical engineer - specialized in the industrial robotic field, 3D designer and modeler (from time to time and some projects I could make the functional prototype too).
I'm doing product design, industrial design, reverse engineering, ideation, etc.
I have over 15 years experience working on various systems/devices across multiple industries, from concept to launch.
1 - double wall is ok
2 - lid/cover/spout also ok
3 - type of glass and plastic/silicone is strictly about what you'll ask from the manufacturer (i will design the parts with respect for the material type, but in the end is only between you and the manufacturer)
4 - sorry, but nothing last forever...
5 - for the lid made of glass will be necessary a plastic/silicone ring or at least a sort of gasket
6 - for a better behavior of the cup/lid assembly while drinking would be preferably to have the silicone ring on the outside...
7 - the mouth piece (drinking spout) could be made to be foldable - this way will make the seal when folded and allow sipping when erected
etc, etc...
Regards
Bogdan