I hate that saying, "I gave it 110%"
You can't get more than 100%, 👍👍
The thicker the tiler the bigger the notch I will use Charlie.
Not saying my way is better, far from it,
If the substrate is perfectly flat then you could use the smallest trowel you have..
I will agree there.
With "these" 10mm trav mosaics I will stick with my 6mm tile as it would normally get cut down for a border & the field tile would probably be done with a 6mm also.
Not everyone uses the same style so I will stick with what I do.. 👍👍
No need to prime but, make sure you have a thorough hoover to get rid of any dust prior to tiling. If your floor is nice and flat, a 10mm trowel will be fine. If there are a few discrepancies, a 12mm may be better.
It depends on the thickness of the mosaic, if it's 6mm or thinner then yes a 4mm is the trowel to use, if it's a 10mm thick travertine then a 6mm notch isn't going to cause problems with adhesive oozing through the joints.