You'll find wineries throughout NZ.

Marlborough is known for its Sauvignon Blanc. Central Otago (Cromwell, Arrowtown, Queenstown areas) is known for it's Pinot Noir. Lots of other wines, though - we really like the dry Riesling of Central Otago too.

Martinborough (NI) is also known for its Pinot Noir.

You don't have to go very far to find a winery in NZ. You don't even have to try, unless you're looking for something specific.

You can't visit Mt Cook from the glaciers, unless you're planning to fly over it. The glaciers and Mt Cook (village) are separated by a mountain range. If you want to visit Mt Cook village, you'll need to take the inland route. If you want to see the glaciers, you'll need to take the West Coast route. To do both, you'll need lots of time as the drive distance is vast.

Not all car rental agencies will let you take their cars from north to south island - some will have you drop off and then pick up on the other island. So, the ferry presents its own hassle factor.

It really comes down to where you want to land on the opposite island - if you want to see Blenheim and Nelson, it makes sense to take the ferry to Picton, but this will increase your drive time/distance in getting down south.

No, three days is definitely not too long in QT, especially when one is spent exploring Glenorchy. Loads to see and do in QT, including a lot of wineries!

We are avid hikers, and many tracks in NZ are stroller/wheelchair friendly. Take a look here for some ideas:

http://travability.travel/New%20Zealand/easy_walks.html

Honestly you are packing far too much in. I see 2 problems with your itinerary :
1. time of year as you will be here at the peak of the season. Can you get a ferry booking? Accommodation bookings?
2. too much driving planned. Car travel is not fun here - winding narrow roads, hills and bends and holiday traffic. It is not like driving in the States.
I would fly Rotorua to Christchurch and avoid the Rotorua to Wellington drive. However this would mean missing Nelson so maybe fly Rotorua to Nelson. I think you should fly some of the way as you will get sick of the driving and being in a hot car. The ferry should not be rough in December.
"To do both, you'll need lots of time as the drive distance is vast." take Mel's advice -if she says its a long way then its a long way (she is American so can judge the distance). I live here and I know it's a long way but people look at NZ on a map and think it looks tiny and they can drive around it in a flash!
On a more positive note there are wineries galore here and my favourites are those on Waiheke and in the Nelson/Marlborough area.

Thank you for the info! I have contacted some accessible vehicle rental companies and will see if we can take the car from the NI to the SI.

I am worried about getting seasick on the ferry but I think it would be less hassle than flying because of the special vehicle rental. If we did fly from Wellington/Roturua to Christchurch then we'd miss out on Wellington and the Marlborough area. But we'd probably add Arthur's Pass. Which option to choose?? So difficult making these decisions.

To break up some of the driving, what do you think of the following SI itinerary?

Nelson / Blenheim
Nelson / Blenheim
Punakaiki
Franz Josef Glacier/Fox Glacier
Franz Josef Glacier/Fox Glacier
Wanaka
Wanaka
Te Anau
Te Anau
Queenstown
Queenstown
Queenstown
Mt Cook
Christchurch

Might subtract a day from the glacier area and add another day to Mt Cook. Or is 2 nights in Wanaka too much?

I understand it's a lot of driving but we really do enjoy scenic drives.

Would love to get more input on any and all accessible sights, trails, activities, etc.

Melnq8, thank you for that link! It is extremely detailed and helpful!

Some more links regarding accessible NZ:

http://www.newzealand.com/us/feature/disabled-facilities/

http://www.wheelchairtraveling.com/wheelchair-accessible-new-zealand-tour-access/

http://www.tourism.net.nz/accommodation/accessible-accommodation

http://www.accessiblejourneys.com/independent/new_zealand/index.html

Two nights anywhere in NZ isn't too much - in fact it'd be a bare minimum for me. Two nights only gives you one full day to explore the area you've come so far to see. You'll have long drive days on most of your travel days, so your arrival day will be pretty much shot. Without that second night, you'd just be climbing into the car the next day and moving on. What's the fun in that?

Agree you are trying to cram in too much "driving and not enough stopping. To paraphrase the Viking River Cruise commercial you'll be "spending more time getting there than actually being there".

When we did our 6 week driving tour of NZ we worked our itinerary so we had no more than 3-1/2 to 4 hours of total "drive time" between stopovers and we spent 3 to 4 nights in each location (with one exception when we drove for 5 hours). The short drive times allowed us to travel at a leisurely pace making intermediate stops along the way to actually "see & enjoy" not only the scenery but points of interest we would have otherwise just driven past. We also, flew between Wellington & Nelson rather than take the ferry. It was very easy to turn in our rental car in at the airport in Wellington and pick up a new one at the Airport in Nelson.

By the way, unlike tasmangirl I really enjoyed driving in New Zealand - the hilly twisty roads were fun to drive and the scenery was spectacular. My only regret about about driving was we did it in an SUV instead of a neat little exotic sports car which would have tripled our fun.

Since we never had far to go we could make numerous stops just to enjoy the view. I tell people that if we stopped for just 10 minutes at every scenic overlook we passed we STILL BE driving around New Zealand. My point being "don't be in such a rush to get from point A to Point B - if you do you'll miss out on so much of what New Zealand has to offer.

It's a great country and I'd go back in a heartbeat.