The Kel-Tecs you mentioned are very snappy and can be difficult to shoot well. However they do excel in their role as a deep concealment carry piece. Since you mentioned the desire to shoot often to familiarize yourself, I would stick with 9mm. Many find it easier to shoot than the 45 you mentioned as well. In my honest opinion, what makes a good carry piece does not make a good home defense firearm. This would also depend greatly upon your usual dress code where you live. For this reason I choose to have a separate firearm for each role, both in the same caliber.