the normal approx thickness of adhesive is 3mm, even using a 10mm float at a 45degree angle you hold the float it will be approx 3mm, the thicker the adhesive the longer it will take to dry...you will possibly need to butter the back of the limestone tiles too as they are porous so you will need more adhesive than you thick.
Regarding tiling the area I would always tile around your floor units, remove the kickboards and tile upto the legs of the units, cut down kickboards and then refit. Pointless tiling under the units not only dont you see them but it cost you money and time laying tiles you dont see
hope that helps
steve SDB Building and Maintenance