First of all, welcome to the forum, Scobie.
That's a big walk you have planned for a winter's day, especially if you take in Ben Macdui. For accommodation, the Corrour Bothy springs to mind, but bear in mind that it could be full, so take a winter tent + camping gear just in case.
I'm not going to advise on the route, as I have not been up Ben Macdui myself, but I would be more inclined to walk in to the Corrour bothy on the Friday, and then tackle the hills to the west, Cairn Toul and Braeriach on the following day, rather than Ben Macdui, before dropping down towards Aviemore. And then only if conditions were good - in poor weather I would most definitely stick to the Lairig Ghru.
PS - I take it that you and your companions have ample experience of walking in winter conditions, and have ice axes and crampons etc?