Needing an in-wall safe: Small for just valuables, or rifle sized?

After years of awkwardly hiding a Costco-purchased safe in kitchen cabinets and needing more storage space, I'm realizing I own my own home and can just get an in-wall safe to hide behind a painting or tapestry. However...Do I keep it small for just heirlooms and documents, or do I move my AR and pistols over to it for a prepped-for-grabbing cabinet while I'm at it?

I HAVE a medium stack-on locker in a guest room closet, been debating adding a lock to that closet door for extra security. However, just hiding the guns and using the locker for ammo and accessories is an option and would warrant less unusual features like the closet lock.

The other snag: I have no idea how much space I have behind my condo wall, for all I know the safe can only be 4 inches deep. That means it'll just fit the gun, the belt kit, and the administrative valuables in a case on the top shelf.