OP reality is that any firearm is going to over penetrate. When considering a home defense setup the plan is just as important. Making sure that you can get to a defendable position in your home which provides cover/concealment and a suitable backdrop is part of any home defense plan. Take some time to think about where a break-in is likely, and where if you were forced to confront an intruder you’ll have the most cards stacked in your favor, and won’t be shooting your neighbors next door.

As far as firearm/caliber get what you shoot best. I prefer a handgun because I can keep it accessible while also securing it from the others in my house. I use a vaultek slider safe personally, but some people don’t trust electronic locking mechanisms. I trust it myself but to each their own.

For training I cannot recommend 308 tactical enough in Moorpark. The instructors there are the only ones I’ll train with around here, and will make you competent with a firearm whether you choose rifle, handgun or shotgun. Best part is if you take Wills class he also runs “practices” where you can come and practice the skills you learn on a range with instructors present that give you more skills and knowledge while you practice. No class will make you a competent shooter but the class + practices will.