You're supposed to buy your gown at LEAST 6 months before the wedding date. I've seen it done 4 months before the wedding, but thats really pushing it! My bridal party/shower is going to be a month before my wedding because my MOH lives out of town.
I bought my dress in October, it arrived in January and I did my fittings in March and June for my July wedding.
My (surprise) shower was 3 days before my wedding, but only because my fabulous Canada friends were waiting for all my other friends & family to arrive from England
I have my bridal party 2 months before. Couples shower 1 month before. Bought my dress 9 months before the wedding.