Good lighting totally changes how a room feels day to day, trading harsh lamps and dark corners for clean, even light overhead. An electrician can usually knock out a standard room conversion in a day or two, and booking during the slower winter months often helps you secure better rates from contractors who have room in their schedules.
Before you commit to anyone, get at least three different quotes so you know what the local going rate actually is. We are looking at about $1100 total for this project, which gives you a clear target to aim for before you sign any contracts.
That 0% window is a hard deadline, not free money, so make sure you clear the balance before time runs out. If you leave a single dollar on the card when the 18 months are up, interest will kick in on the whole original amount.