A strong handgun and shotgun should suffice for the basic home arsenal. You want powerful, close-range tools. A .357 gives you a choice of ammo (.357 and .38 spl) and a Mossy 500 is one of the best values in firearms, period. It'll fire a tremendous range of ammunition, reliably, with minimal maintenance, and you can easily build it out as a tactical shotgun over time.
My concept of the well-rounded arsenal includes non-firearms as well - stabbing, thrusting, and slashing weapons; mace; swinging and clubbing weapons; throwing weapons and a variety of implements ranging from full-sized to concealable, located throughout the home. To my way of thinking, you never want to be in a room and wishing you had a weapon nearby. There should always be a strong tool at close hand.