I had a similar thing for a birthday, around 20 people. Some vegetarians, a couple of downright picky ones.
It was a hot day so a cold buffet, saves messing about with cooking, heating etc.
Made several different breads, bought baguettes, cold meats, chicken, made a fish shape on an oval platter with smoked salmon. Lots of cheeses, various salads, quiches, potato things, crisps, cheese traws, crackers, snacky things, sausages, sausage rolls, cheese & onion, Quorn 'sausage rolls' and snacks. Just made a long list of what would work and raided the supermarket. Tarte au citron and cheesecake went down well.
I did make a slow cooker full of soup, made it first, blended and put in to keep warm and left it for people to help themselves but no other cooking other than a cake.
Everyone had enough to eat, plenty to take home for those that wanted to (close family) and some for us for the next day.
Also had some cake and fancies brought by guests.