Project idea: Upgrade old MTB to road groupset for commuter?
V brakes and mechanical MTB discs aren't compatible with normal road levers. You'll need either V-brake specific drop bar levers or cantilever brakes.
Road cranks have narrower chainline and larger chainrings and MTB chainstays are wider. You may run into compatibility issues here, too.
You probably won't be using the highest gears anyway, since Marathons or Gatorskins have huge rolling resistance compared to proper road tires
Fast, potholes and rack don't fit together. Get a messenger bag or backpack instead.
Drop bars and road components aren't going to make you that much faster. The most difference is in ergonomics.


What I would do would be MTB groupset with road cassette, V-brake compatible levers and bar end shifters.