Remember, you'll need to re-adjust the saddle height when you switch to cycling shoes - almost always lowering the seat. Cycling shoes are designed to be as close to the pedal spindle as they can make them to be and they don't have the thick sole non cycling shoes do. You'll almost certainly be too high when you switch to cycling shoes. Also, lowering a seat often entails moving the saddle aft on the rails since because of the seat tube angle the seat comes closer to the handlebars as you drop it.

MTB shoes are almost always a respin on an equivalent road shoe when you are looking at all but the lowest end shoes. Usually the even are virtual copies of each other except for the sole. So you won't find that one is considerably wider or fitting different than the road version. The good news is that when you find a road shoe that fits, you can usually go look at the same mtb shoe.

FWIW, I take a dead nuts normal width shoe (i.e. not wide or not narrow). I have a heck of a time finding cycling shoes wide enough to be comfortable for the mileage I put in to the point where I'm pretty much resigning myself to looking at custom shoes. Width isn't the only issue for me, but finding wide shoes can be tricky. There are a number of spd based shoes that are set up for commuters but that is not going to have the stiff sole you'll probably want when you start putting in lots of miles.

There is nothing more fun than a new bike except for a new bike you've gotten a bunch of miles on and you and it understand each other.

J.