Congrats Steelhead on your Fleet purchase, your gonna love it. Terry and the gang over at FWC are very easy to work with and will help you on your questions.
There have been many fine articles on airbags vs overload springs vs rear spring set upgrades on wander the west and as always it depends on your application. My Eagle shell is bolted down full time to my 2013 V6 Tacoma Access cab so I opted for a rear spring upgrade (1500 pounds), It rides very stiff empty and absolutely fantastic with the camnper mounted. My upgraded Eagle shell weighs 900 pounds dry with my portable Engle refrig/freezer on board. Though it is portable I leave it in the truck because I have an injured back and can not lift more than 25 pounds.
While you are trying to decide, weigh the truck empty with a full gas tank. My truck weighed 4200 pounds, plus 900 pound camper = 5100 pounds dry. When I travel solo for a week to the hot springs adding 300 pounds of water, food, beer, etc I am probably over the max 5500 GVRW rating of the truck. There is a formula that figures a portion of the rear bed weight is carried by the front wheels, however I don't know what it it? Since I'm only over about 5% of the year I'm not too worried about the wear on the mechanical parts,
I just purchased the Engle because no matter what I do ice only lasts 3-4 days and then I'm eating out of cans. I ordered my Eagle with a solar plug on the roof and on the back wall. I have tested the Engle on 12 volt only after I first brought the temp down with 110volt. It lasts 3 days too short a time to sit parked for a week, so I will be ordering a 80 watt panel soon.(I only have lights and a refrigerator to run). I decided to run it as an accessory off the back wall plug to see how often I park in the shade. I can always mount it on the roof later.