Wow!
I remembered I shot my first wedding with almost the same set up as you. I was using a EOS300 with Tamron 28-200 f3.8-5.6 and built-in flash! Even as a back-up photographer, its a disastrous set-up! Maybe I can share my experience.
For the day event, you may need about 3-4 rolls of ISO400 films, get 1-2 more spare. Because you are using built-in flash, be mindful of the hard, black shadow (sure have one) cause by your len and lens hood, so you have to work in your "crop factor". What I did was, ask the lab to scan into CD and recrop all the images. As a back-up photographer, just shoot the "side stories", like relative chatting with couple, brothers resting or smoking outside the house, the auntie that hold the tea ceremmony, the sisters giggling and whispering to each others' ears about a cute guy, enjoying the buffet, the driver of the bridal car etc. Just don't shoot what the main photographer shoot.
For the night, prepare 3 rolls of ISO1600 or ISO3200 film, use the remaining ISO400 films to shoot the reception before the dinner, the prep for the dinner, people discussing about the schedule, people seeing the photos of the couple etc. When the dinner starts, change to ISO3200 film to shoot people eating, chatting, waiter serving, guys pouring each other with beer etc. Don't shoot those table to table group photos, let the main photographer shoot
At the end of the dinner, shoot the groom's drunken face, shoot the empty ballroom, after event like punishment of the groom by the brothers etc.
My first shots' result is not that bad. In fact, after a lot of encouragement from friends that saw the photos, I took a course with Stanley Lim Colour Centre for wedding shoot. Now I free lance as a wedding photographer, but of course, not with my EOS300 and Tamron 28-200 anymore lah.
Hope this help and enjoy yourself!
Max
ps: remember the shadow of the lens cause by your built-in flash.
