Firstly, good luck! Lots of really great advice here. Order your turkey from your butcher well in advance and think also about what other meat you will be needing, so you can order that too.
Plan all the menus for all the meals you will be serving while you have guests. I always do this, not just at Christmas, and it's really helpful to see how the whole thing "flows" if you see what I mean. I see nothing wrong with Boxing Day being a left over day, with lots of cold cuts, ham, salad and pickles etc - we love this and I almost prefer it to the dinner itself. All you need is a nice hot pudding (something easy like a crumble, or do the Xmas pud - I find that too heavy on Xmas day itself).
Once you've got your menu planned, you can then look at the shopping list and work out also how much you can do in advance/freeze.
Don't forget to top up on all the non perishables well in advance like mayonnaise, crackers, bin bags, batteries etc. We always cook our turkey on Christmas eve and it makes it so much easier. It smells lovely while we watch Muppets Christmas Carol and sing along. Then on Christmas Day, it is easy to carve and you have far more room in the oven for spuds and other veg. On Xmas Eve itself, we eat special seafood platter - usually lobster, or oysters, or mix of nice shellfish. This is great, as it looks v poncey but is actually no hassle to cook. We often order the seafood platter from Marks but if you have good fishmonger, they could easily do something like this for you. V simple and really has the wow factor.
Also sensible to plan in advance your alcohol/drinks requirements. Usually find that most guests are happy if well lubricated, and less likely to notice any mishaps in the kitchen! Surprising how much wine/gin/mixers etc you get through so would advise getting in a case or two from someone like Laithwaites.
Finally, am very soppy and if we have any guests for Christmas that are actually staying on Christmas Eve, then they will always wake up on Christmas morning with a stocking. 
I love doing this and find it great fun - a tangerine and a bag of chocolate coins are of course obligatory.