Body panel spacing. How big is too big?

If you get the hood square and get a nice, even gap with the cowl, at a distance that you like, leave it on the car. You don't need to paint the bottom of the hood off of the car. It is actually nicer if you leave it on and do the entire engine bay with the hood and fenders on.

If you don't want to do a K member drop to install the engine from the bottom, there is a way to do it from the top side without removing the hood, after everything is all done.

You should be able to adjust the front of the fender in and out after you've put the apron bolts on (most of them across the top, that go in from the engine bay). The bolts at the radiator support will allow you to move the entire fender in and out with the bolts at the top completely attached. The aprons are designed to flex, so you can put seam sealer on them without shims to get the front wheelhouse/ fender to seal and not get the engine compartment full of splash.

Fit them first, after making your adjustment to the top rear of the fender and once you like how it fits to your gapped and square hood against the cowl, take them back off, put seam sealer on the edges that meet the aprons and reinstall them.