When should you start shopping for the bridesmaid dresses?
Immediately, although you should make sure you have a general idea of what you want. If you and your bridesmaids are not ready to purchase yet, you should at least start browsing. You never know when you will find the dress that you have to have.
It can take a bit of time for the dresses to come in, whether you order them in person through a dress shop or through the internet. Once they do come in there needs to be time for alterations to be done. Usually the dress needs to be altered initially to fit the bridesmaid and then again when you are closer to the wedding date.
This is not advisable. Just like in the rest of the fashion world dresses become unavailable either because of high demand or because they are discontinued to bring in new stock. If the bridesmaids order separately it is possible that some of the bridesmaids will not be able too get matching dresses. Another thing to consider is that even if you are able to order all of the same style they still may not look exactly the same because they could come from different fabric dye lots and the coloring could be different. . This is not something you want to happen when you are looking for uniformity.
The bridesmaid dresses are only one part of the bridesmaid outfit. She will also need hair accessories, jewelry, shoes and an evening bag. You may want to wait until the dresses are in hand before choosing some of these items. You should see if you can get swatches of fabric with the dresses to use to match the color if you are to dye the shoes or the evening bag.