Re; cabinet sizes:
When we ordered our all cherry cabinets in 2011, there were two height sizes available for over a refrigerator, or range hood vent. The larger would have been too tall for above the range, unless mounted closer to the ceiling. We didn't want stepped cabinet heights, so we got the smaller size. Now our microwave is two inches higher than our old one was with the former oak kitchen. They were NKBA certified, mid grade cabinets, with vinyl veneer end facings.
Our new ones are made for Thomasville by Masterbrand, in Indiana, and Illinois.
We mounted the new cabinets the same level above the counters as the old ones were.
A neighbor has older similar cabinets as we did. They replaced their standard vent hood with a microwave recently. Now when they use their gas oven which has it's vent on top, the fan in the microwave runs all the time on it's own.
That means it is too low over the range. Maybe the microwave sizes are taller?