Tell whomever stamps the plans that this is what you are planning to do so he can engineer that closet accordingly (unless its on a slab).
And for anything that has valiue, buy a real safe, TL15 or better.
I am the one doing the plans as well as the construction. Shouldn't be enough weight to impact the foundation wall. So don't need to change anything with the foundation guys (only part of the addition I am not doing myself).