When should I start looking/purchasing a dress?

It will probably take you a month or so to find the dress you want and then it can take 4-6 months once you order it for it to be delivered. Then it will take time to alter it (they all need alterations) and you want to allow some slack in here just in case... So, I would suggest starting to look for a dress as soon as possible. Think about the size of the dress and if you are going to lose/gain weight before the wedding. Buy the closest size to what you will be at the time of your wedding. Look in the Advice section in EZWeddingPlanner (top menu bar) and check out Bridal Attire for lots of good info about dresses.