Yay! How exciting! I guess the main thing to ask is how much you anticipate it costing, and how long the alterations person will need. Ask whether you can/should book all your fittings in now, well in advance (I know mine books out) and what they would prefer you bring to each one.
My advice would just be to take your time! Make a list of questions beforehand so you don't feel stressed afterwords. If you have a mom, MOH, bridesmaid, etc. with you ask them to take videos of the bustle. AND SOAK IN EVERY MOMENT OF YOU IN YOUR GOWN!! You won't get that time back.