There are a lot of things to do and take care of when planning your special day.
Many couples book the reception venue first - this is highly advisable as many can be booked out up to 2 years in advance.
It is also very important to book your celebrant. Yes, there are a lot of celebrants to choose from, but you need to be comfortable when appointing that person to officiate at your ceremony. The longer in advance you book them, the longer you have to get to know them.
On engaging your celebrant, a Notice of Intended Marriage is filled out with that person. A celebrant needs to sight your birth certificate or passport, photo ID such as a licence or photo card and any divorce papers if either party have been previously married. This NOIM must be filled out no later than one month prior to your big day but can be filled out 18 months in advance.
Keep this in mind and things will run very smoothly for you.