Let me start out by saying that we have rescued 4 PMU mares (Percherons) and their foals, so I do have some experience in this. I also have owned (and still own) many drafts/draft crosses. Not just one or two but several. We currently have (on my property) 4 draft crosses, my daughter also owns (on her property) 2 draft crosses and at this time has a belgian (who has ESPM) Her Percheron just passed this spring. Not including those we have rescued, rehabbed and rehomed.
What peggysue is talking about is ESPM. Espm is a heredity disease, meaning that he would get it from his parents just like HYPP or HERDA. If he doesn't have it, you don't have to worrry about it. He is does have it, it can be controlled with diet generally. I would cross that bridge when you come to it. But I would read up on it just in case. Drafts, and ALL horses IMO (and my vets also) need mostly a diet of hay and/or pasture. As he puts it, "The grass/hay is the meat and potatoes, the grain should just be the dessert". A good quality horse hay should be most of your horses diet. Be careful in using supplements, especially on the foals, you can really mess them up (growth, bones, joints) if done incorrectly. (too much of one, too little of another)
As for shots, it varies for the region, I would ask the vet what he recommends. We are in TX and the basic minimal shots I would recommend for the winter season is VEWT and Rabies. You may want to do others when the weather gets warmer (west nile etc) Again, your vet is the best person to ask.
We worm all of our babies with Safeguard monthly for 1 year, then aprox every 6 weeks there after (due to our warmer weather).
As for what to do with him. Personally, I WOULD keep him confined in a smaller area for a while. I would start out in a stall (if you have one) first for at least a week, longer if he is very wild and doesn't want to settle down. Then, as you get to know each other and trust each other, put him in a larger area such as a small paddock, then a larger pasture etc. If you just immediately put him in a pasture you will never catch him to have any interaction with him! Believe me, even a 1 acre pasture is large if a horse/colt doesn't want to be caught. The key to all rescues, but especially PMU rescues is patience, patience, patience. Being that you are getting a foal, you should have an easier time of it. The mares who are older take more time since it is many years with little human interaction. But, that too can be done. One of our PMU mares went on to become a Mounted Patrol horse, another was used for Jousting and competitive shooting. The other two were steady trail mounts. It is definitely worth the time and effort.