Another vote here for getting a notebook and heading it up with each day that you will have guests and a section for breakfast, lunch and dinner on each day.
Most days breakfast will probably be toast, cereal, fruit etc. Christmas Day we have rolls and sausage so add that to the shopping list (saves having to do a proper lunch if you've had a big breakfast!)
Christmas Eve I usually do a braised beef casserole of some sort that can be made in advance and heated once DS is in bed - Christmas Eve dinner we have a 'grown up meal'.
Christmas dinner is traditional. Don't bother with a starter. In fact we just do some nibbles and fizz around lunch time, dinner at 5pm and then cheese and biscuits later if anyone is hungry.
Boxing Day is leftovers and pickles/salad etc. I usually do a ham just before Christmas as that does for lunches Boxing Day for those that are sick of turkey.
We will still have guests on the 27th so by then we usually book a pub lunch somewhere and get out for the day.
Don't be afraid to ask for help - peeling vegetables, washing up, putting someone in charge of wine. Equally, if guests offer to bring something take them up on it - crackers, tin of biscuits, Christmas cake, maybe a dessert?
Just as aside, the first year I had Christmas here I tried to be hostess of the year. I did it all myself, refused all help and assembled a Christmas menu that looked spectacular but needed hours in the kitchen. By 7pm on Boxing Day I was an absolute wreck and in tears - no fun at all and I learned my lesson!