Christmas dinner is not complete without the trimmings and those trimmings are often very personal and reflect back to the Christmas trimmings you had as a kid. If you are inviting guests to the big day whose background you don't know then it may not go amiss to just ask them if there are a few Christmas dinners trimmings they see as "essential" to make the day, if the answers are obscure ask them to bring the ingredients, all guests want to provide something anyway. I think there are some obvious ones which we'd all agree to:
Let people have what they want and have all the main options available (as with the brown sauce). However nowadays most people will go for some form of wine with the main meal. Fortunately turkey is a robust old bird and will go with white and red wine. White better with the breast and red better with the dark meat but both work. I have some favourite pairings in mind but I think you are better off going with your own favourites as turkey is really flexible and giving on this. Perhaps a glass of champagne or good cava would be the ideal accompaniment given the occasion?