That 16 gun safe will hold 12 comfortably, if you're lucky. If you have bolt rifles or optics, maybe even fewer than that. You may need to remove the optics or bolts if you plan on filling it up. By the time you add any ammo, personal valuables or handguns you'll discover just how small it really is.
You made a good choice, but don't be surprised if it's all a tighter fit than you expected.
I have a 36 gun safe, and I had to remove all of the bolts from my rifles to get them to fit into mine. I took business cards and labeled each bolt so I would be able to match them up to the rifles later. I tied the card to the bolt with some strings so they stay attached.