If you peel the potatoes and parsnips the night before, leave them in bowls of cold water and cover with cling film.
I put the parsnips and potatoes in at the same time as the bird, and keep en eye on them, then take them out when they look nearly done, then they just need to go back in for 20 minutes or so to finish off, while the bird resets (covered in foil and a couple of clean towels), and you cook the other veg.
Oh - and I parboil the potatoes (boil them for 10 minutes) then drain them and give them a good shake in the pan, to chuff up the edges so they go more crispy, and then put them and the parsnips into really, really hot fat - I have a big chef’s pan (a deep frying pan) so I do it in that - I find it easier - but you can put the tin in the oven with the fat in, and put it on the hottest ring on the stove when you put the potatoes and parsnips in, so they sizzle and go crisp. Do this carefully - the hot fat will hurt if you splash yourself.
Don’t put too much stuffing in the cavity of the bird - fill up the neck end (where the flap of skin is), and do the rest in balls or in a separate dish. Really filling the bird means it has to cook for a lot longer, and that can make it dry.
Do as much as you can the day before - I make the stuffing and stuff the bird, make bread sauce and gravy, prep all the veg (I do roasties, parsnips, sprouts and chestnuts, and red cabbage), and make the brandy butter to go with the pudding.
Above all - don’t worry - it is really just a roast dinner with a few more bells and whistles, and you will do fine.