Usually it is the stock tires that determine the payload rating for a pickup truck along with the passenger capacity of the cab. If the tires will support the additional 200 lbs. I would not worry about the rear axle and wheel bearings. Another way to approach it is to look at the Ford GCWR for the truck which includes the truck and passengers and load in the box and any towed load. That number provides a maximum total load that the truck's engine and transmission and frame and suspension can safely handle.
If you have a 2WD truck the easiest and cheapest approach is to change the rear tires to gain more load capacity. The rear wheel wells should have room for much larger tires. Your speedometer may be off by 2-3 MPH at freeway speeds and the gearing will be a little higher but not a big change from the stock configuration.
The payload for a crew cab includes 150 lbs. for each seat. A truck that holds 3 passengers has the payload reduced by 450 lbs. and you will see this difference if you look at two otherwise identical pickups with one having a crew cab and the other a regular cab.
For a truck battery there is no reason to waste money on an AGM battery at twice the price of a sealed flooded lead acid battery. I buy Interstate batteries from the locally owned and operated NAPA dealer. I like to keep my money in the local economy and not have it go to the Walton billionaires in Bentonville. My Interstate batteries have without exception lasted for 5 or more years. After 5 years I replace them with a new one and trade in the old one to be recycled. No need to make it complicated unless you like that sort of thing and everyone needs a hobby.