No need for the semi-auto. It's just an uneeded luxury that will add on hundreds. The handicap of the pump will only make you better with accuracy. Go for a pump 12 gauge if you go for a shotgun. I suggest the 870, because it's extremely reliable, and cheap(250$ new). Also, in a home defense situation, just yelling to leave and pumping the action could send the invader on his way. If you may hunt larger game like deer, it'll be tough because the rifles necessary for those won't work for small game. But for small game I would suggest a .22LR as well. The extremely reliable Ruger 10/22s fetch for about 250$ new as well. But because you are going to go for birds as well, the shotgun seems like the best gun.