As for bolting directly to concrete. One big factor is where do you live and the other is how old is your house? If you live in the desert and own a newer home like I do you can bolt directly to the concrete the humidity is low and the moisture in the concrete is also low. There is a plastic liner under my concrete and above the ground that helps keep moisture below the concrete. If on the other hand with out that plastic liner and in a humid area the concrete will act as a wick and hold some amount of water. Even on a painted surface it will over time do some damage to your safe and may make the finish look bad near the floor. In which case you would want some sort of barrier between the concrete and the safe something like a sill plate gasket, plastic, or other material. Wood would be one of my last choices without plastic sandwiched between two pieces. Wood will ROT if placed directly on concrete that holds moisture. That makes it a wick in my book so I would look for another product. Those pads that you stand on for work that are about 1 inch thick might be a good idea. I'm sure there are other product like it that might be good choices. A smitty pan for a washing machine might work. My point is that you want separation from any source of moisture.
Earlier I also asked about std wood floors and what floor of the house. If you are placing a very heavy object on a floor over time the floor may show signs of sagging. You may/may not be able to see the effects but a little reinforcing in the area to displace the weight over a larger area might no be a bad idea. You can do this in a number of ways one place a large piece of heavy plywood under the safe to spread the load or support the floor from the underside. I have seen equipment moved through businesses that fell through the floor. I'm not saying it will happen but it might.