Gail,
As I remember, your little orphan is already eating from a bucket, right? Once the feeding problem is taken care of.......then, expect to worm and vaccinate a little earlier than you would other foals.
As has been posted above, the other important thing is to make sure your foal KNOWS THEY ARE A HORSE. We were fortunate that we had a filly born within a day or so of our little orphan guy, so we made him spend most of his time with that filly and her mom. He was also turned out with the moms and babies on pasture daily. Yes, he knew he was "special".....and still does, but he gets treated like a horse too.