I want all the emails that Auctiva send to my customers re: (default winning bidder, default payment reminder, default address request) to be customised by me. I can only seem to apply a customised winning bidder email to my preferences and I would like to know how to make sure that my customised payment reminder & customised address request are the only emails sent to my customers.

Can you please tell me exactly what page i need to go on the auctiva site to to add my personalised payment reminder & customised address request emails to my preferences?

Go to the Sales tab, then click Manage Email Templates.