A photo booth keeps guests busy and gives everyone a souvenir from the night. You should book this at least six months out to make sure your top choice is actually available for your date.
Since this is a flat cost, it fits neatly into a payment plan. You can use the Citi Simplicity® Credit Card to hold the expense while you pay it off in smaller, manageable chunks before the wedding.
Remember that the 0% intro window is a deadline, not a gift. If you still have a balance after the 18 months are up, the bank will start charging you interest on whatever remains, which can get expensive fast.