Contact the school you are considering enrolling him in and ask them about their policy dealing with children with severe food allergies. An Allergist is also an excellent idea too. Look into IEP and 504 plans and start getting set up for this stuff now while you have the time to look into it all. And there is some hope that he may outgrow his severe allergy once he gets a bit older :)
Check out http://www.kidswithfoodallergies.org/ - Parents of Food Allergic Kids.
Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication Allergies, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD (Lupus?), Osteoporosis, Anemia, Very Low Lymphocyte Counts (T-Cells & B-Cells), malabsorption/malnutrition, possible Lyme Disease (Igenex Lab IgM WesternBlot positive), etc.
Meds: Pulmicort, MaxAir, Injectable Vitamin B12, Herbs, Nutritional Supplements, Essential Oils, Homeopathy.