Switching from straight handle bar to drop down - which dual control lever would fit?
What you are proposing to do is basically impossible. There is no documented compatibility between Shimano mountain and road groupset components.

The derailleurs have different actuation ratios (how far the cage moves for a given length of cable pull). MTB and road cassettes have different sprocket spacings. I've not read about anyone experimenting with Shimano road levers and MTB hydraulic brake calipers but I'd bet they are not compatible either.

You cannot  replace the entire drivetrain and brakes. An 11 speed cassette may not fit on a MTB freehub body and a road crank won't fit in a wider MTB bottom bracket shell, and if you are contemplating buying a whole now groupset, just buy a whole new bike! 

Another reason to not attempt this is that flat bar bike frames typically have a longer reach, as the distance from the head tube to the flat bar grips is shorter the the distance from the headtube to the hood or drop hand positions on a drop bar. Flat to drop bar conversions typically need a very short stem which can negatively affect the steering.