Lot's of good ideas here, however I think that in any small scale skirmish, you have to think of the battlefield in terms of a layer of rings. High Power rifles for the long distance threats of 250 yards or more, so you would be talking about .50 BMG (expensive), .338 Lapua (also fairly expensive) .300 win. mag. (moderate expense) 30.06 (affordable weapons & ammo also very common), .308 win, and finally .280 or .270 (also affordable weapons & ammo .270 ammo more readily available). Intermediate range - weapons like assault weapons AR's, AK's, SKS's for your intermediate ranges 250 yards to 75 yards. Close range weapons shotguns and .22 LR for 100 yards and under. CQB and "In your ****" ranges handguns .44 mag, .357 mag, .45 ACP, .40 S&W, 9mm Luger. This is a good example of defensive weapons and ranges if you are in a fixed position against superior numbers in defensible positions.
Most of these weapons can be had at fairly reasonable prices. If $$$ are the limiting factor, personally I would select a proven platform in shotguns like Mossberg 500/590 or Remington 870/1100. A good rifle like a good used Remington 700 or, I know this will be controversial Remington 7400/742 that's proven in calibers like 30.06, .308, & .270 win. The point in selecting is what you're effective and comfortable with and what platform will have ammo readily available w.t.s.h.t.f. One other criteria you have to consider is how many people will have to be outfitted? Will you have to hump all this weaponry long distances? How much ammo will you be able to carry on your person if you have to bug out. In a bug out situation you have to consider weight, because I guarantee you after 15 to 20 miles of hard humping in a day, you are definitely going to want to lighten the load. If you are being pursued, you will lighten your load and the last thing you are going to want to leave behind is your weapon. Lot's of people bitch about our military going to the 5.56mm as our primary infantry weapon, but the fact of the matter is, is that you can carry a lot of rounds that are effective out to 300 meters by your average shooter with moderate training. It's the jack of all trades weapon particularly if you have to hump weapons, ammo, and field supplies for long distances. Sidearms - (Please see above) One or any combination of the above could be suitable depending upon the person. If you have minimally trained people in the group, you can't go wrong with shotguns using a combo of slugs and buck or bird shot. If using birdshot I wouldn't go any smaller than no. 4 or 5 shot. However whatever you have on hand would be better than nothing. Maintaining these weapons will be a factor that should also no be over looked. The simpler the better if dealing with moderate to minimally trained individuals. Just my 2 cents worth.
Mr. T
NRA Life Member