Within Netbookings settings it is possible to enable which fields are mandatory for guest creation in front end and back end, for waivers and voucher creation.
If you want to send payment links automatically using email reminders - and allow guests to settle payment before arrival - utilise Letters, Reminders and Payment Links together to achieve this.
A Pricing Group can have a 'Deposit' amount or percentage set, that will be required at booking (online or via staff), instead of full booking payment.