Absolutely, and remember that a safe should be bolted down, ideally to a large concrete slab. Here in the north that means the garage or basement, and a safe that goes into the basement isn’t coming out easily unless it’s a walk-out. In the south I know it’s more common to have the first floor on a slab so you have more options. But basically, a safe should be on a concrete slab, wherever that is in your house.
Yes. Anything with a pistol grip takes up extra space, and anything with a grip and on optic takes up double. I think the # of gun ratings are plausible if you own only iron-sighted bird guns and old style rifles. For longer term storage you can pack guns in tight by having them alternating left/right and even muzzle up/down, but that is not convenient for access.