Because I do not like risk, I prefer to book and ticket my itinerary as soon as possible, to lock in the fare. If you ticket with any of the major OneWorld airlines, there isn't any realistic risk of the airline going broke. In theory, you can issue a ticket with open-dated flights at the end, but in practice this is difficult (some airlines can't/won't do it). What I do is figure out my desired dates for the first set of flights, then pick dummy dates for the rest of the flights. These are dates chosen simply to be able to have a flight booked, preserving the desired stopover versus connection status of each airport. Once all my dummy dates are within the booking window of the airline, I book and ticket. Typically this will be ~10 months before my first flight. Closer to departure, when the remainder of the flights are bookable on my desired dates, I have the airline change the dates. This is free.