A high-speed mesh router is an investment in your home's connectivity that should last you at least five years. Focus on buying a system that handles your current device load so you do not have to replace it when you add more tech later.
Wait for late autumn sales when retailers clear out inventory for newer releases. Last year's model is often just as fast and costs significantly less than the latest version on the shelf.
That 0% intro APR is a deadline, not free money. If you have a balance left after 15 months, the bank will start charging interest on whatever is still owed.