This has been a dilemma for a very long time. Getting as many guns in a safe as possible, and still allowing ready access. They are contradicting goals, no matter how you play the game. I designed the Barrett Slide-Out, not for gun density, but for convenience. The trouble is that there are too many variables with so many weapon profiles. If all of the guns were basic AR15s, easy cheesy. But look at all the various gun types, then layer that with optics and other tactical add-ons. The skews are nearly infinite. That's why we started putting a few long guns holders on the back of the door, so you can have quick access to a couple of key weapons, and not worry about the rest.
My safe is packed with too many rifles, along with other items I need to store securely. I gave up trying to find a perfect arrangement, and I bought a few 6-packs of gun-socks. Now I just pack then in, some barrel up, some barrel down, some sideways, some front-back ways. The gun-socks prevent any damage if you don't get too sloppy in handling. In a space where I had a formal rack arrangement holding 11 guns, I can now pack in 15-16 comfortably and still leave a couple favorites loaded in front ready to grab and go.The gun socks have label tags, so I mark them with an appropriate description to help find things.
I have said it before. I'll mention it again. Your Gunsafe is no place to store bulk ammo. If you're like me, that's not a small space that is being wasted. 6-8 ammo cases is a big chunk of real-estate that can be used for more important stuff. Keep in mind one of the reasons you bought a safe... fire protection. It doesn't make any sense to put all those beautiful firearms in a box along with a powder keg of live ammo. If you do have a big fire, the risk that the ammo becomes a flame thrower inside really defeats the whole purpose. Ammo should be stored in a place where it will do the least damage if the worst happens. Put it in the Garage, in an insulated cabinet if you like made from several layers of drywall and a padlock for security. It can be replaced. Sure, keep a few loaded mags and favorite pistols, and/or a go-bag with whatever you think is necessary when the Zombie Apocalypse happens. Be practical, and make the most of the space by only storing the things that are worthy of the security. If you're rich, buy more safes... if not, be frugal and practical.