How many think a 3 gun set up would be the perfect core to a home defense, self defense, shtf group of guns?
What would make this set up the most practical for real life and competion? What would you use?

It would be a good start.  I'd favor a can over a muzzle brake on the AR for home defense, but a Limited Division/Tactical Optics type set-up would be good to go.  By shooting 3 gun you will test your equipment/ammo for function and get them zeroed.  Just this will put you leaps and bounds ahead of the mass of shooters.

I've been thinking about part of that a lot, how much would we stick our necks out by using NFA items for home defense?

The idea of one pistol, one rifle and one shotgun wouldn't necessarily be a bad core grou of weapons for SD but the best? Possibly but not necessarily but honestly its too hard to say because there are way too many variables. "One size" does not fit all when talking about SD weapons.

Now, even assuming a 3 gun assortment was optimum for everybody, some of the dedicated weapons used by a lot of hardcore 3-gunners would not be the best choice. A lot of the handguns used for 3 gun would be next to impossible to CCW with. Some of the shotguns have ridiculously long mag tubes and some of the rifles are geared more towards precision long range shots and are not all that well setup for CQB which is the more likely way an average person would use a rifle for SD.

Depends on the division you're shooting for. Production or Tactical, absolutely!! Open or limited, maybe not so much.

Yes I definitely meant tactical or irons division.

Then I can't think of a better way to equip yourself and train.

Too many people focus on what gizmos they have or what caliber they're using and don't realize that the most important thing to master is accurate fire while under stress or on the move. Competing in matches is the best way to pursue that goal (IMHO).

Here's my new 6.8mm AR, I'll be changing my M4'gery some to more closely clone the 6.8.
I also have a Glock 19 and am trying to come up with a plan for a shotgun.
For price and practicality I'm thinking a Remy 870.

NFA is fine for self defense as long as it is a good shoot.  Having fired rifles indoors while double plugged, a can is your friend.

Indoors it sounds like a can on a SBR maybe your friend.