Oh, so you don't really want advice, but are just looking to start another .223 vs. 12 ga thread? Lol - never mind.
Glenn stated my position better than I did with one sentence:
Too much gun choice and not enough training, IMHO.
Either gun (or caliber if you want to boil it that way) comes with limitations and possibilities that thier operator needs to be aware of and understand. That is the most useful thing these kind of threads do - bring those things to light so they can be studied.
But the race between these two types of weaponry is close enough that I don't think it matters which you choose - just what you do with it afterward. Pick the one you like best...
Then study it and its limitations and possibilities. Master it and when those limitations and possibilities crop up you many have a chance to work around them...
As for you current list of "limitations and possibilities:"
"- a .223 ovepenetrates less than a .357 Mag with the right ammo;" *** unless you need/want penetration, then you should load a different type of ammo
"- a .223 offers 1.700 joule of energy (triples a .45 handgun)" *** Energy is relative and worthless if you can't hit your target.
"- a 12ga is unbeaten in destructive power at short ranges, offering 5.000 joules (10 times .45)" *** See previous possibility.
"- a 12ga offers multiple hits with one shot," *** And multiple misses - besides at close (HD) ranges those several projectiles act as one...
"- 12ga slugs would surely overpenetrate," *** Unless you really want/need penetration, then they're a great ammo to select.
"- you cant accurately and selectively shoot bad guys who are close to good guys (which you can with the .223)." *** Huh? At close (HD) ranges those several projectiles act as one... and a slug at thirty feet or less (HD range) would certainly be as accurate as a .223 if the operator and equipment is top notch...
Anything can be argued by anyone, but real trainning and practice require a choice and commitment. Choose one and go with it - master it and its limitations will become less and it's possibilities greater.
YMMV...