I have catered to individuals before - the boyfriend with a peanut allergy was pretty safe at my place since I rarely eat peanuts myself (and no peanut butter at all!), and my cookware is almost all stainless anyway, so it's easy to allergy sanitize. I was able to host a celiac guest - flour isn't really something I use all that much since I don't bake often. I made meatballs that a friend on paleo could eat when we went to a potluck.
I would not be able to host someone who kept strict kosher, unless I bought the food prepared elsewhere and used disposable plates and utensils - meat and dairy have been combined many times in my house. I doubt that I could adequately meet halal restrictions either but I don't know as much about them aside from the slaughtering procedure.