I recommend that you start setting it up now. No need to be too ambitious either. Start by making a list of 10 people and email them or message them and ask if they will be in your book launch club. Make note of them in a list or a spreadsheet. Once you have your first 10, you can always add more. Something I would have done differently for my own: start sooner and over-time build my list up to a group of 50.