A door ding is an eyesore that catches every bit of light, but it doesn't have to ruin your bank account. Paintless dent repair is a specialized craft that pushes the metal back into place without needing new paint or body filler.
Shops are often empty during the coldest winter months, so that is when they are most likely to offer a deal. You can usually get a single panel repair done for about $250 if you ask during their downtime.
The 0% window is a deadline, not a gift. If you still have a balance once the 18 months are up, the bank will start charging interest on whatever is left, which defeats the purpose of the plan.