Once your place on the trip is confirmed, you'll be able to choose all of your booking options. If you've made all the selections you need, you're welcome to pay your balance in full at any time before your payment deadline.
Paying early won't incur any additional charges, so if you'd prefer to get everything paid off sooner, you can do so.
Some event add-ons may become available at a later date. If this happens, you can simply log back into your booking, add the event to your trip, and pay for it separately when you're ready (subject to availability).