You should be fine preparing all of the veg tonight and leaving it in water. At least, that's what I do and I've never had an issue. For the potatoes, parboil them and do the initial roasting in goose fat tonight if you have time. Whack them in the fridge and then take them out again in the morning and finish them off in the oven using some of the fat from your turkey/meat of choice. It's a Jamie Oliver trick I found a few years back, swear by it for every roast dinner.