Not recommendations, just some things to bear in mind.
Road miles in the north west are not like road miles elsewhere, don’t try and cover too much, or you’ll end up spending your whole time driving.
Lots of places, even more so on the islands, will be shut for the whole season, check before you go.
Don’t try and do too many islands either, as you won’t have long enough on each island to capture the atmosphere.
In terms of recommendations, I wouldn’t go to Harris in the winter, it’s a phenomenal place in the summer, when you can get out and explore all the wonderful beaches and awesome bike trails, but risky in winter. Lewis is bleak, and not particularly beautiful, an acquired taste IMHO. I’d be inclined to stick to Skye, mull and occasional jaunts to the summer isles etc.
There’s always next time for the rest.