A solid multi-room audio setup is an investment in your home, not a disposable gadget. If you buy quality components and in-ceiling speakers now, you shouldn't have to touch them for a decade. Focus on brands that prioritize open software standards so you aren't stuck with obsolete tech in three years.
Wait for the mid-November sales to pull the trigger. Retailers often clear out last year's amplifier models to make room for new stock. These older versions usually sound just as good as the newest ones for a fraction of the cost.
That 18-month window is a hard deadline, not free money. If you have any balance left after the 18 months are up, the bank will start charging you back-dated interest at a much higher rate. Set up an auto-pay for at least $70 a month to ensure you clear it in time.