[RPKESQ]

If you are really new to firearms. Buy a .22 rifle. Much easier to learn proper safety (like muzzle control) and operation with, as well as it helps to build confidence because it is so much easier to learn to shoot well with it. Then progress to a .22 handgun. A semiauto is fine at this stage. Again, go through all the same steps as with the rifle. You can practice quite a bit as .22 ammunition is very cheap. If you can shoot a .22 well, anything else is doable with just a little practice. You can pick either rifle or handgun for well under $500 (in fact you should be able to buy both for about that price).

A centerfire semiauto pistol will not be the best choice to learn with. Keep that choice for later. Just like learning to drive well, you don't start with GT2.

A shotgun is very poor choice for interior home defense. Few people know weapon retention techniques or proper tatics in interior home defensive situations. And don't listen to the "just rack the slide and bad guys will run away" crowd. They have learned their tradecraft in movies and TV. No reputable firearm training organization teaches such claptrap.

Which brings me to the final point. Learning to shoot well is a different and easier skill than learning to defend yourself with a firearm. The first is simple technique (like playing horseshoes), the second is full of variables that have almost infinite possibilities (more like chess). A good training course is essential (google: gunsite).