A quality OLED television is an investment meant to last you five to seven years, so buying the right model now keeps you from needing an upgrade next season. Focus on the picture quality and gaming specs that matter to you so the screen feels fresh for the long haul.
Wait until the November holiday sales to pull the trigger. Retailers drop prices on high-end tech then, and last year's models often hit their absolute lowest price while still offering top-tier performance for most gamers.
That 0% window is a deadline, not a suggestion. If you still have a balance once the 18 months are up, the bank will charge you interest on the remaining amount, which can get expensive very quickly.