Welcome to the forum.
As your question(s) is state specific have moved this thread to the Missouri sub-forum.
It involves real estate law as well as gun laws.
That said, your home (apt) is generally considered your castle and don't believe you will find any laws restricting gun ownership, possesion, or mode of carry. Laws generally do not tell you what you can do, but rather what you cannot do. Therefore the absence of a law forbidding something makes it ex post facto legal.
Sure that others will chime in shortly.