Keeping shotguns loaded for self defense in the house do's and donts?

I want to keep my 12 gauge Mossberg mariner loaded for self defense in my house. I am familiar when it comes to shooting them but still could use some schooling. I am looking up things online as well so this post is to see other opinions of owners. First question is, is it bad to keep the tube loaded with a full five shells? Second is how long should you keep the same five shells in it before replacing them? And last I have heard that shells can fire if the shotgun is dropped..is that only if there is one in the chamber? Or is this more of a myth that isn't even really possible