That's part of my problem... the bottom 2 shelves have papers and a fireproof doc box. Mine is supposed to be a 12-gun, I'm lucky if I can get 8 or 9 jammed in. Bolts, oprods, a scope or two... everything gets in the way.+1 on the bigger the better idea because you may not only store your weapons in there but valuable papers, keys, etc.
With dial combinations you need to write it on the side of the safe more times that you would like. I'm into bigger than you need today, because you will fill it up faster than you think.Electronic locks are nice, they are quicker and simpler to use. However, if they go out, you are stuck with a safe you can't get into. Which means drilling the door, and then installing a new lock. Or just place a 9 vol. battery to the face and punch in your numbers and your in. In 12 years, my 9 vol battery has gone out once, plus I open the safe once or more times a week. Once inside you can replace the 9 vol battery.
Dial combinations will probably last forever, though you should change the combination once a year to prevent wear on the internal parts.
Ask me how I know all this.GI9