Wee done most of the itinerary you mention but it was in summer.

Some thoughts

Nelson is a very nice town. We liked it so much we have returned several times. It has a nice mix of arts food and natural beauty. Abel Tasman is really nice and there are a lot of options for a day trip short to longer hikes a variety of boat rides available we did kayaking but im not sure itcan be done in the winter and we found it much nicer than Marlborough sounds. We spent a day at the farewell spit sandbar which we terrific. Tours run based on the tide and you are pretty much alone with amazing sand dunes.

Drives in nz are deceptively long and not like road trips in the us on straight freewAys at high speed. Roads are narrow and very curvy and you can not go at high speed. And part of the experience is stopping along the way at scenic points small towns etc.

As for Milford I don't know your budget but an option is coach one way and plane back. It's a pretty awesome flight at low altitude between the mountains. We've done a Milford overnight which was ok. Doubtful sound was a more beautiful and special place IMO as there re less boats on the water

Have driven queens town to Christchurch when fog cancelled our flight. And queens town to mount cook. Stayed at the hermitage. Again lots to do. Hiking stargazing at night. Rafts on the taman glacier.

Unless you have a real interest I'd skip the wineries.

Drove the west coast last year from greymouth down. Really enjoyed it if you like scenery and no billboards gas stations just the great outdoors.

Most of the beauty of a new Zealand experience is enjoying the ride and scenery and partaking in activities. Don't plan a route where you're always in a hurry to get to the next place without enjoying the Moment.