Definitely tackle one thing at a time as pp have suggested. Looking at the big picture will just stress you out too much!
I'd start with save the dates because you want to let your guests know asap the resort, location and date.
As far as dress shopping, my friend and cousin both bought sample dresses that they were able to take home the very same day. There are also rush fees if you decide to order a dress. There are options for you so don't stress out too much