I don't see a problem with expansion on your project. The walls sit on the slab, and should not separate from it. So will the stone once affixed to the wall.
But, on the other hand, if you think water will get on the porch and it slopes towards the house; then you'll want to go with the caulk idea. I have seen a lot fail at ground level in a 'freeze/thaw' situation. But Nashville? Probably not
As far as the windows and doors, just run the stone up to the trim. There really isn't a concern for expansion, and you have already done the 'house wrap' for the seal.
And hey, if you own a tile saw after all those projects at home, it will cut that cultered stone REALLY nice!..................BOB