A used Ford F-150 is a workhorse, but it comes with real costs beyond the sticker price. Expect to pay for higher fuel consumption, routine maintenance on a heavier chassis, and higher insurance premiums than a standard sedan. If you want the best deal, wait until late fall when dealerships are desperate to clear out inventory before the end of the year.
Negotiating the price and figuring out how to pay are two different battles. You should walk in with a clear number in mind and focus on the out-the-door price rather than the monthly payment. Once you have a firm price, you can decide how much to put on a card and how much to cover with a traditional loan.
The 0% window is a deadline, not free money. If you have a remaining balance after the 18 months are up, the bank will start charging interest on that remaining amount immediately. Have a plan to pay it off entirely before the clock runs out.