First off, congrats on getting your horses home.
Second, that all seems kind of small. The stalls at an absolute minimum should be 10x10 and even that is kind of cramped space. The 6-7 foot aisle is going to be a pain, it doesn't leave much room for working aorund your horse, but it is doable, again, at least 10 feet is ideal.
The pasture space is also pretty small. The dry lot may be ok, but it doesn't leave much room for 3 grown horses to stretch their legs and run if they so choose. The 1/2 acre will be eaten down in a few days of half day turn out and you'll be left with another dirt pen.
It it possible to make the stalls 10x10 and the aisle 10 feet wide? That still only calls for a 20x30 barn... Stalls all along one wall instead of on both sides of the aisle.
Is it possible to turn the horses out with the cows? Around here, horses and cows get turned out together regularly. The horses may be a bit scared at first, but they usually calm down within a day or two.