Of course you don't have to commit right away, but if you love a style and need to grow it out or get a cut, always consult with your stylist to get you there. Bring pictures of styles that you like and of course the picture of the dress. Any headpiece or tiara should be mentioned in the consultation so the stylist will know what's the best placement for it.
If you don't have 8-9 months to grow out your hair, extentions are another option to get the length you're looking for. And it can also help clients with thin hair. Extensions can be the permanent bonds or the temporary wefts. Again consult with your stylist.
Then discuss your color, cut and conditioning treatments. Remember, your stylist needs time to perfect your wedding day look.