you can purchase a duplication tower, but they can get pricey especially if it's only a one time thing that you need it for.
it might eb cheaper for you to send the job out to a service to do. create the one dvd then pay someone that has the equipment to duplicate it.
please please please use good quality media. a wedding is so important and people want these discs to be readable after a few years...go with taiyo yuden or verbatim. if you decide to send the work out to be duplicated ASK what they use for media.
as far as converting avi to dvd you have a few options
avi2dvd, winavi, nero vision express among others.
try to do a software search on www.videohelp.com for avi to dvd and you should get some good software and some good guides as well.