Birdshot
Buckshot
Slug
In that order.
Yup.
Yes, except for the slug...not enough practice, plus the heat of the moment and intruders' movements. Birdshot shows the police you were willing to try a non-lethal load at first. After that, all bets are off and Buck up next.
I practice with my 870 every year or so at the local gun range. A couple things I've learned from those training sessions other than what Navy taught me:
1. With shoulder position you can get a better bead sighted shot, it takes longer to position and louder for your ears and the recoil can knock you off your sighting.
2. Under arm position is not as accurate, but if firing a 12 gauge, well, with the light and general sighting, still good. Plus, you just let the recoil swing backward under the arm.
3. The one I like the best is the "hip" position. Most people aren't trained for that because it is the least accurate and you need to keep the shotgun 2 to 3 inches from your body so as to avoid recoil on your hip. Like number 2., just let the recoil follow its open path with your arms swinging in tandem. The upside is quick positioning, quicker re-loading, and less sound pressure to the ears.
Whatever your experience with shotguns, get the blinding light attached at the end. It only takes a second to reach forward to turn on. It also comes with a cable you can run up to your receiver. I prefer turning on manually. I don't want a wire I have to trust is still attached during a surprise dark encounter.
Some of the stuff I’ve got falls into the “exotic” category.