Mike, great trip report, excellent photos and obviously a grand adventure!
Both of the Hobie carts will carry a pretty good load. the newest Trax cart is rated up to 176 lb. (I've overloaded it to 190 lb. on smooth ground). It's great for uneven terrain and soft sand -- rolls easily. The down side -- it cost a bit more, you can get a flat and it's hard to extract from under your loaded kayak in the water. If you get this one, make sure you get the new more durable, easy rolling, higher capacity wheels (shown here).
I use the standard cart most of the time -- light and rugged
It easily hauls the 115 lb. Adventure Island (shown here with my older narrow frame cart)
and an Oasis with ballast and gear (about 140 lbs). I've hauled as much as 190 lbs with it for short distances. No problem with flat repairs, easy to extract and insert in the water (it also floats), but doesn't give as much of a cushioned ride as the Trax and doesn't work nearly as well in soft sand.
How much you can load on your boat probably depends on the distance and terrain. Stringy has much more experience in this area, both with Hobie and custom carts, and hauls his boats around on carts all the time. Perhaps he will share some thoughts on the matter.
Looking forward to your next trip report!