For the microwave venting, the first question is does it sit on an
outside wall? If Yes then your in luck. Just vent it out straight from
the back of the unit. If not, you can go through the roof.
Whatever you, make sure your stove sits between 2 wall studs if
possible so there will be no obstructions for the ductwork.
Thats the dilemma I had. When I gutted my kitchen, I found that the
new location for my stove had a stud in the way for a vent. My
original design had 15" cabinets on either side of the stove, but I
changed them, shifting everything over 3"( 12" cabinet on one side,
18" cabinet on the other) so my stove can be in the middle of the
studs. Just a suggestion if you run into the same problem.