I'm with all the others who recomend training first. Newbies who aren't properly trained can develop a lot of bad and unsafe habits and the only way to prevent this is with good sound training.

As for a Home Defense gun, I cannot think of anything better than a 4 inch K frame in 38 spl. As for why, it's a relatively quiet caliber that is easy to master. I also learned that mastering a double action revolver resulted in my becoming a much better shooter with every type of firearm.