Keep in mind that you will be putting other valuables in the safe so get one larger than what you think you'll need. Some insurance companies might even give you a discount because you have a safe.
I use the large silica bags (in boxes) to soak up any moisture rather than an electrical device. In 25 yrs I've not had any moisture damage problems. When the indicator turns pink (instead of blue) you put the bags in the oven for a few hours and that drys it out and it's good for another 3-4 months. Got mine at Cabela's.
Always go bigger. Much bigger.
A good safe, especially if you are INVESTING in something in the 1,000 pound range will last you a lifetime and then some.
Everyone has personal preferences but I like the combo dial. The ones in the 800+ pound range have locking dials and you can 'day lock' them.
Electronic locks lose a layer of security and eventually, they will fail. With combo locks they will last for thousands of openings and as they start to fail, you will notice it. It won't be like the electronic where one day the just stop working.
Anyway, it's a great idea. Maybe you'll get a gun or two to help defend yourself and the house too