Smart dimmers change how your room feels at the tap of a button. You can set the mood for dinner or brighten things up for reading, all without touching a switch. Installing these while you are already painting is smart because you will have the walls open and the power off anyway.
Aim for the slow season in early winter to hire an electrician. Pros are often looking for work then, and it is the best time to negotiate a lower rate for the install. Get at least three quotes before you commit to anyone.
That 0% window is a deadline, not a gift. If you still have a balance on the card after those 18 months, you will start paying interest on the remaining amount, which will cost you more.