Additions to Booking System Software including Royal Mail Postcode Lookups

Our current booking system is based on PHP. We are looking to add a few extra features to the system. 1. A discount feature is already built in to the system but needs looking at as it doesn't total up the prices correctly on the booking confirmation page and the email sent to customers. 2. Integrate the Royal Mail Postcode address lookup feature ([login to view URL]) so customers can enter a postcode and the rest of the address is auto filled. 3. Currently if a customer enters a postcode that we do not deliver to the system still allows a booking to go through, we need to put a fix in place to stop this from happening. 4. On the final booking screen, once the customer presses confirm booking a white screen appears while it's going through. About 6 seconds later the confirmation page appears. It would be nice to have something displayed in this 6 seconds like a scroll bar saying processing or something so the customer knows something is happening. At the moment people keep pressing refresh as they think its not working.