A good multi-room smart speaker system fills your home with sound and should last you a decade if you pick the right ecosystem. Buying once means choosing hardware that won't get abandoned by software updates two years from now.
Wait for the big mid-summer retail events to buy, since manufacturers often discount current gear to clear room for fall refreshes. If you don't need the absolute newest badge, last year's model usually drops in price and sounds identical for hundreds less.
The 0% intro APR for 15 months on purchases and balance transfers is a deadline, not free money. If you still have a balance left when those 15 months run out, the regular interest rate kicks in on the whole original amount.