IMHO the more you can do in advance the better ... I have done roasties in advance before .... just roast a little short of perfectly done, chill, bag freeze - and bring them round for 20 mins in hot oven on the day to crisp up and brown off ..... in fact, I always have roasties in the freezer like this - makes for a quick meal with left over meat etc ........... stuffing too .... that gets done in advance.
I do all my veg (apart from the potatoes) in steam bags then keep them in the freezer till the Big Day. I also do the stuffing and freeze it uncooked, likewise the pigs in blankets. But I use the juices from the turkey to make the gravy and I wouldn't dream of cooking that in advance, so I wouldn't be able to go freeze the gravy. No reason why you shouldn't, though!
Actually it is an excellent idea. The fat solidifies and you can then lift it off the top in one go, (and spread it on stale bread and put it out for the birds).