I have done some extensive research as well. We have plans to spend 1 week on the South Island.
Day 1 fly to Invercargill from Christchurch, rent
SUV, have lunch at Batch, check out the Burt Munro exhibit at the hardware store then head to Te Anau. On the way we'll stop at Te Waewae and McCracken's Rest for unparalleled beauty.
Day2 an overnight Doubtful Sound cruise
Day3 maybe a short drive up the SH94 and then to check out the bird sanctuary (Punangu Manu)
Day4 drive the SH94 to Milford Sound stopping along the way for a quick look at the departure point for the Milford Track, Mirror Lakes for the short 5-minute walk, The Divide to have a sit at the shelter (maybe walk the trail for a few), stop T Pop's view, and another stop at the Homer Tunnel. After the cruise, we'll head to Invercargill maybe stopping at the Croydon Aviation Heritage Center. I hope to shop at The Lost Gypsy Gallery.
Day5 we'll spend exploring the Catlins: MacLean Falls, Purakauni Falls, and hopefully Nugget Point Lighthouse
Day 6 fly to Christchurch, rent car, drive Arthur's Pass, visit the Hopkitika George, and stay in Hopkitika
Day7 up to Punakaiki for the Pancake Rocks and Poroari Track. Well stop to eat at Stella Cafe then stop at Castle Rocks, Porter's Pass, and maybe Lake Pearson. We return the car and head for home next morning.
Any suggestions for me?