A:AnswerAccording to the installation diagram, the 30" is from the bottom of the cabinet which would be the top of the microwave. Since the microwave is 17" tall, you should have at least 13" clearance from the stove-top to the bottom of the microwave. You should be fine.
A:Answerpeculiar question - there is built in kitchen cabinet above - guess if you remove it? But still the bracket holding the micro. is at the bottom -
so, do not understand what would be a benefit? Perhaps attachment of two holding screws at the top could be easier, but you still need the
bottom of that cabinet (and the rest of that cabinet ) to hold micro.?