While you're over in Iraq, jumping out of airplanes, try to find a way to get some horse-keeping books to read.
Cherry Hill has several that are very good for beginning horse-ownership. Her website is:
http://www.horsekeeping.com/
Where is the property? You also need to check your zoning to see how many hooved animals you are allowed per acre, etc.
But, if you have 6 acres, your best solution is to fence the entire thing (perimeter fence) for safety, then fence some smaller sections so that you can rotate pastures. And, horses are herd animals and prefer having buddies.
Feeding hay all year around is a good thing to do... sometimes different grasses can cause illnesses in horses - depends on the kind and time of year, age of horse, breed of horse, etc, as to how they are effected. Some grasses are not good for pregnant mares.
So far as oats... they are an okay feed, high in phosphorous, so they may have to be balanced with other supplements depending on what kind of hay and what kind of grass is in the pasture. There are many pelleted feeds available that are good and offer a variety to target young horses, pregnant mares, old horses and just plain dumb horses. : )
Some people will have a barn or run-in shelter with a "dry lot"... a small area where there is no grass, and then turn the horse out on grass pasture overnight, or for short periods of time, etc.
There are many ways to manage pasture and feed horses. I'm sure you'll hear from many others. GOOD Luck and keep safe.