Additional Thoughts
The more safes, the more difficult it would be for burglars to do a clean sweep. They don't have the time to either crack two safes in place or attempt to cart them off.
The separate building could be a problem if it has easy vehicle access. If the burglars have adequately cased the job and show up with a truck with a hydraulic lift gate, the safe is theirs if they can free it from the floor.
If you have excess capacity in your safes, consider adding several hundred pounds of lead ingots to each. Once you get a safe to around a thousand pounds and throw in a staircase in the upward direction, only a professional safe mover can get the safe up and out. My 1050 pound safe, damaged in hurricane Sandy, was hauled away by professionals. They used an electric stair climber resembling a miniature tank, to bring it up the basement stairs.
As others have said, layer your security: alarm system, fortified doors, concealment, etc. I've never built a safe room but if I did, I would forget the cement blocks, put up forms and use poured concrete with rebar. You'll need to work with pros to insure that the safe door and poured structure may be joined together.
If your workshop resembles Home depot as mine does, all tools that can be used to attack the safe or its mounts must be out of sight, elsewhere in the house or under lock and key.