Hi Fourkidletts,
Your F150 is practically the same as mine (with the exception of I have the larger bed) right down to the color. I tow a 6000# tt with a 4 adults in the cab with absolutely no issues at all. It is rock steady on the road and had gobs of power to spare. When not towing the 36 gal tank yields almost 600 miles to a tank.
Yes, a full tank of gas is considered intopayload. I’m not sure how much the spray in adds, but it is worth it. I’d stick with the wheels that come with the truck.
Enjoy your new ride and tt!