I've been making the same decisions since July. I knew nothing about guns, but I've learned a lot in the past 2 months. My wife and I have taken a concealed handgun course, and we've purchased two pistols. I'm now considering a shotgun for home defense. Please read the topic that I posted, "Home Defense Shotgun suggestions": I received a lot of good recommendations. Also read the excellent article about home defense shotguns at this link:
Since you've taken a concealed carry course, I'd advise also purchasing a handgun if your budget allows: it's especially nice to have protection when you're away from home. For concealability and power at a not too bad price, the Glock 26 (9mm) or 27 (40 cal.) are hard to beat: they're small but very controllable.