Dd has an intolerance to pretty much all highly processed foods (if it is processed but contains whole, real ingredients, it's fine, but when it's made with a laundry list of chemicals it causes many problems, including night terrors, agitation, and severe eczema). I find that this is the, THE most complicated restriction to explain and have anyone accommodate. If someone asks, "are crackers O.K." the answer is not a simple yes or no. For that reason, I really try to do what I can for others, but never expect others to accommodate us. "Homemade from scratch" to others often means chicken and cream of chemical soup in a crockpot, and "homemade from scratch" means something vastly different for us! Luckily, many people we socially interact with know what we mean by "from scratch" and we don't have issues for dd. So, obviously it can be difficult to have real clarification, but I think it's worth it to ask the guests.
For allergies... I try to really ask for details because I find that the term "allergy" is used SO often for "I don't like" or what is actually an intolerance. For one, cross-contamination is very important and in the other, cross-contamination is not a risk. I have a true food allergy, but I just break out in hives and wheeze a little. It's not life-threatening, but serious to me. Still, I wouldn't ask anyone to avoid that ingredient when cooking. Finding if things are truly an allergy and their severity is important, but again, can be difficult to know the details.
Religious accommodations... I may or may not be able to. For example, dh is from the middle east... I cannot provide halal meat because of where I live (we have no halal butchers within reasonable driving distance). In this case, I serve whatever meat I'm going to serve and make sure I have plenty of sides that can come together to make up for the lack of meat.
My favorite way of entertaining, though, is a cocktail party where I don't have to make a full meal and can have a great variety of cold and hot hors d'ouevres. It's also easy to avoid cross-contamination. With this game plan, I can almost *always* accommodate everyone. TBH, entertaining was much, much easier 20 years ago... I don't remember anybody ever having allergies and few dietary restrictions (veg*an being, actually, the only one I ever remember having to address back then).