Congratulations on your first house! I think you made a wise decision when you nixed the OTR MW/hood. The vast majority are not very effective as hoods and that location for a MW is far from ideal.

Our family ranges in height from 5'10" to 6'6" (and growing). Our vent hood is 42" wide x 24" deep and is mounted 30" above the cooking surface of our 36" electric cooktop. The only time anyone has bumped their head on the hood (that I know of) is when my 6'5" DH stuck his head inside the hood to look at the "squirrel cages"...he didn't lower his head enough when he backed out and bumped the back of his head on the hood.

So, I would say you probably don't have much to worry about. We did, though, get a hood without sharp corners "just in case"...you might consider that.

Additionally, I suggest you look into a 24" deep hood if you do any high heat/stir fry/high smoke/etc. cooking. Basically, if you do more than boil water.

You want the hood to extend 3" beyond the front burners for better capture. If the above applies to you, I also suggest you get a 42" wide hood so it extends 3" out on each side as well.