An 18" barrel...minimum legal length without NFA hoop jumping...will suffice for most social discourse. Shorter barrels are more easily handled in tight spaces, but they increase noise and recoil, all other things being equal. We used them for breaching and CQB because that is ALL we used them for. The guys manning roadblocks, etc. used Mossberg 500/590s as a rule. Even the PSD kids carried stocked, standard length guns.
Longer barrels are better for bird hunting, but if you can sneak up on it, an 18" will probably kill it. I understand and support the Migratory Bird Act, but if I am in a survival situation...
The 1911 is accurate to about 15-25 meters on a man-sized target for most folks who are properly trained. I know guys in various small units who, given a customized gun, can do much better than that. But I always tell people that a handgun is just my short-term solution to get to a long gun. The M1A Scout is a very nice little rifle and can easily fill the bill from 50m out to 300m (or more depending on skill level). But longer distances are not really 'self-defense' distances unless someone opens up on you from that far out and appears to have some skill and then keeps coming at you.
I think statistics indicate that most 'self-defense' shootings are in the 11 meter or less range. A good handgun will suffice for that and the shotgun may offer more of an advantage if handled correctly. One school of thought offers that a submachinegun is even better in the HD role. That could be extended to SBRs for those not up to funding a full-auto purchase.
If someone is shooting at you from any range, I would suggest it is a good idea to presume that they are "very serious about killing" you and react accordingly. The further out they are, the more likely you are to evade them. When they get close, you lose that option.
My AOW goes into a custom shoulder rig that hangs under my right arm with a holster for a 1911 on the weak side. That allows me to be very 'well heeled', as the saying goes down here, and I can cover it with a light jacket or loose shirt as I am a large SOB. With a tactical vest, the shotgun goes into a rear-mounted scabbard and the pistol goes in front on the left side. So close up, I don't have a problem.