I was looking into the Flash line system but I wasn't sure about the breaking ability of tiles over 10mm, that being said I'm having trouble cutting 1200x600 10mm tiles lengthways on my Sigma 1280 due to them being so strong and brittle! I had to cut them with my Rubi TC 125 hand held wet saw.
How thick is the ply on timber floor, is the timber floor solid, if not you're right rip up and replace with 22mm no more ply, if it's solid maybe replace it with same thickness cement boards, level everything and Ditra or Dural mat the lot.
10mm trowel minimum and skim the back of the tile with adhesive, if you've already got a 6mm trowel and don't want to get a new one, 6mm on the floor and 6mm on the back of the tile but it could be messy!
I have laid them on floors a few times, but 6mm trowel on the tile and 10/12mm on the floor.
Just make sure the floor is level and use lots of leveling clips.