Guess my main thought is... don't overthink it too much for a short trip, though good planning makes a world of difference. Any multi-day travel on the bike should be enjoyable unless you get it completely wrong.
August is going to be cold... still winter, if your lucky might get good dry weather... regardless you'll need damn good gear and be well prepared for some miserable conditions if you are unfortunate enough for it to turn bad.
Using layered clothing can make a big difference between comfort and misery.... one extra light top can add that few degrees body warmth.
Plan shorter day rides depending on how much your wife thinks she can handle... it may be 3-4 hours in the cold and that might be more than enough for her.
I haven't done the route your thinking of, but have done some big trips with the wife on the back (round Oz, Tassie in Nov), and its pretty tiring on them just hanging on. Plenty of stops in order to keep the co-pilot comfortable.
Extra gear... carry a puncture kit, just in case. Easy enough to use and better than being stranded.
Have some decent size zip ties and maybe some gaffer tape with your tool kit. Amazing what they can fix in a pinch.
Maybe carry some spare gloves in case it rains heavy and you can't get them dry enough for the next day's ride.
Try to find hotels or motels where you'll have cover for the bike, even if its just underneath the verandah. Nothing worse than packing up in the rain to have to do a days ride.
That's a few late night thoughts....