How much food per guest?!
Answers:
Your starter should be small and tasty. It's intended to whet your appetite for the main course and not fill you up so keep it small and light.
Main course; Approx 100g protein per adult, 75g per child is about right, 2 tablespoons of a veg is one serving. Serve 2 veg plus potatoes, rice or pasta Approx 75-100mls sauce/garvy per person. Having some extra for "seconds" is often a good idea if you are not if your guests are big eaters.
A choice of dessert is a nice idea. Try making one cold one which can be made the day before and stored in the fridge, and one hot one cooked whilst the main course is being eaten. Have one much lighter than the other so smaller eaters or health conscious can go for that option.
Good luck.
The secret of a good dinner party is forward planning and keep it simple if you are not confident so you can enjoy it on the day. Have fun