It looks like you decided on the Remington 870 as your first weapon: a good choice.

For the second, you may want to consider if any second long gun is practical to carry given the circumstances you envision. Carrying 2 long guns could be a bit of a burden.

So I would agree on a handgun as a second, and a .357 lets you use a variety of ammo, from .38 wad cutter, shot and up to full power .357. It gives a lot of flexibility. In this, it has similar advantages to the shotgun. Personally, as I mentioned in your other thread, I would go with a 6 inch barrel: I think 3 inch is a bit short. 4 inch might be a reasonable compromise. Also, you might find a good used .357 at a very reasonable price.