It's great that you're doing your homework before going down the road
I was in a similar situation as you are last year. 4.0L, V6 4 Runner with factory hitch.
I had to upgrade my factory hitch to something rated at 500#. I did have a truck frame that was approved to work with a WDH. My friend has a Highlander and they are built on a Camry frame. Toyota does not recommend using a WDH on them.
However, many people on the Toyota forum have been fine with a lightweight system in your range.
After reading this thread, I would only have the following adds.
1. Check with your local dealer service manager on his/her take on using a lightweight WDH system on your vehicle.
2. Your Curt hitch rating seems fine.
3. This is the WDH that I purchased and it has done a fine job combining WD and sway control. (just check brackets periodically to make sure nothing shifts)
4. etrailer.com has some good articles and videos on WD and sway control systems. They also seem to have a knowledgable staff that will take calls directly to answer any questions.
5. Make the time to visit the CAT scale to weigh you packed out rig after you get it set-up. If you're not 100% packed, you'll still get the 80% knowledge for 20% effort. Tell your wife it's important for the safety of your family and not a waste of time. Have her go with you so she gains an understanding of the process and she can calculate the numbers as you get them :-)
If that doesn't work for you, plan an extra 1 hour and hit a truck stop on your 1st outing to get the fully packed out weights. It's really no a big job and will give you and your wife some practice hitching and unhitching the rig. Just take your time and have patience. I think our CAT scale process took us all of 1/2 hour total.
In the sticky section of this forum, there is a worksheet for getting CAT scale figures.
I just re-arranged the order of weights to minimize hitching and unhitching.
1st weight is TV + TT + WDH engaged
2nd weight TV + TT + WD bars removed, but stowed in TV rear cargo area
3rd weight TV only (unhitch TT off the the side of the parking lot somewhere out of the way)
Here is their website for locating your nearest location
They also have some tips for the weighing procedure and a nice video.
Three weights will cost you $16, best money you'll ever spend.
Bring a yard stick with you to reach the call button. It's about 8' high usually designed for tractor trailer rig heights :-)
When all done, your towing experience will not be the best, but it will be safe and within the design limits of your tow vehicle.
These TT's are like having a parachute behind you. Wind will be your enemy. Leave early morning (6-7am) and arrive by noon.
Don't be in a hurry. You'll have more control and best gas mileage doing 55mph and just stay in the slow lane.
CA law is 55mph when towing. I went from Ohio to CA and back doing 55mph. Arriving safely is the key to an enjoyable trip.
Keep us updated, post some pictures and your scale readings when all done.