Thinset and shower fall

Gday,

I am tiling over tiles on a shower floor. The waterproof membrane has been installed.
I need to change the fall to the drain; which to complicate things is not center.
I want to use thinset to do that. I have a few questions if you know the answers.

1] is the finished height of a 12mm sq. notch trowel 6mm or 4mm?

2] is a 10mm layer of thinset too thick when laid in one go?


3] if 10mm is too thick what will be the result when laying a 10mm bed of thinset?


4] if I build the thinset in 4 or 5mm layers, will the layers bond to each other if smoothed off?


5] if the layers should not be smoothed off, what method would you use to rough up the thinset?

.....keeping in mind the need to maintain thinset height integrity.

6] which tile adhesive would you recommend for the purpose?