In my opinion, nothing is overkill when it comes to a WDH and sway control. Safety is key in everything, especially when towing all your gear and precious cargo (family).
Is your Highlander FWD or AWD? If it is FWD, I would not attempt to tow without a WDH. Although, I still suggest it with the AWD model. Dry hitch weight is 305 on the 184BH, but you will never be that low. As soon as you add your gear to it, that number goes up quickly. Now as far as the Reese brand WDH is concerned, I am not too sure how adjustable it is, since I used a different brand when I had my bumper pull unit. If it were me personally, I would go for it. Can't go wrong with Reese, Husky, Equal-i-zer....all respected brands. Just remember to keep an eye on your total weights and the limitations of your tow vehicle, and the 600/6000 should suit you just fine.
Welcome to the Jayco family, and don't forget to post pictures once your unit comes in.
2013 Eagle Premier 365 BHS
2012 F-250 FX4 Lariat 6.7 Powerstroke Turbo Diesel
5000# Super Springs