My first response is that once you know the relationship you are in is directed to the path of courtship and marriage then it is safe to start making plans towards your dream day. Of course, wedding planning is a process and everything will never be finalized in a single moment. An ideal time to start planning is one year before the wedding date. However, some couples start planning two years in advance and even as little as three months. Cutting it close to the date is a huge risk but it’s not impossible. Venues are normally booked out quite early as well as other key vendors like wedding planners, photographer, Caterers, DJ/Band, Officiant etc. You may be forced to change the date of the wedding to allow more time to adequately plan.
Some ladies wait until an engagement has happened whilst some start minor planning before engagement and once that has passed then planning takes on full speed ahead. For instance, a couple can already decide on a prospective date and start making plans to book a venue, photographer and deciding on a bridal party. After the engagement, the photographer booked can have the engagement photo session done. It is recommended that the same wedding day photographer is the same as the engagement photographer as it allows you to familiarize yourself with the photographer and builds great rapport. You will get a far more relaxed feel on your wedding day as the pace was already set. The fact that your venue was already booked you would now start to plan towards bridal attire, catering etc.
Be a forward thinker and define your goals and make plans towards it. As I said once you are clear about your relationship and you have that special time of year you know that you want to be married then give your self a year to start making plans.