We (family of 4) have spent a fair bit of time in the Grandby over past several years, including a 6-week long roadtrip from AK to America and back.
As far as "camping" goes,
the things we use the most are: water for cooking & showers, kitchen sink for cooking & cleaning, hot water heater for showers and dishes, furnace, refrigerator.
Assuming you will have similar needs with the trips you have planned, and if you like projects and want to spend time planning, ordering, building, etc. and think you can do better than the folks at FWC who have years of experience and continual improvements, knock yourselves out with a shell. If you want to focus your time on using the rig and enjoying the outdoors, then buy it with what you need.
Then get a truck. It's kinda like getting the cart before the horse, right?
Personally, the camper is a light load for my 3/4 ton truck which I use for all sorts of hauling and towing. Oh, and on that 6wk trip - we averaged 17.5mpg. I've never owned a toyota, but can't imagine they would do better than that with a heavy camper on the back.
Have fun!