I have experience with making a bad decision with a safe. I thought I was being frugal and bought mine after shopping around from Sam's club. Good quality safe, but it has the electronic keypad. I didn't give any thought to things like EMP or CME, which are not likely, but entirely possible to cause the electronics to not work.
Keep in mind that just because a safe has so many slots for long guns it may not be able to hold that many if you have things like large scopes or bipods on them. I am constantly juggling mine around trying to keep them from getting banged by the next one.
I would suggest a manual locking mechanism, as large as you can afford. Don't sell the fire rating short when considering your purchase. Don't just think of it in terms of fire, it is really a heat protection rating. Some types of fires can smolder for a very long time and raise the temperature in the structure without flaming, but still cause considerable heat and soot damage.
We went on a structure call a few years ago where a large candle was left burning on a dining table when the occupant went to bed. Luckily she closed her bedroom door and it kept most of the IDLH stuff away from her and she was rescued. The rest of the house was a disaster. Melted plastics in the kitchen 25 feet away, very fine soot everywhere, discolored glass on exterior windows, it was a mess. A light fixture in the room of origin was melted at the ceiling as well. A good safe should protect from an exposure similar to this. Good luck.