1) I would start out with Timothy Hay, or some other grass hay. You can always add something like Alfalfa if he starts loosing weight.
2) The rule is about 2% of your horses body weight, so about 20 pounds. You can take some hay or add some if he/she starts loosing/adding weight.
Also, here is a great article also, http://www.humanesociety.org/animals...e_feeding.html
Make sure your horse is fed often, at least about every eight hours, however, I would definitively get a small mesh hay net, it stretches out the time that they take to eat the hay, and you can feed probably 10-12 hours. Make sure your horse gets a couple hours of turnout each day, if he/she stays in a stall with no run, 8 hours of turnout is the minimum you want to go, but if you ride 1-2 hours each day you can bring it down to 6 hours. If you have any questions, feel free to message me, and welcome to the forum!