I'd think twice about this. Lots of folks seem to want their buddy with a nice DSLR to shoot a special event, but this kind of thing needs experience more than fancy equipment. But if you insist ...
See if you can go to the church and check out the lighting in advance. Bring your gear and take some test shots, when nothing is going on, if they will let you. That will tell you a lot.
Assuming you will be permitted to take flash pictures, I'd think you might want to step up to getting a couple light stands, radio triggers, two powerful manual flashes, and modifiers. Those don't have to cost a lot. Having a powerful lighting setup also means more even lighting, which will make everything easier for you.
You will also need gels to color match your strobes to the ambient. Those are cheap.
I'd suggest you check out Neil van Niekerk's website:
http://neilvn.com/
and his Tangents blog for interesting articles:
http://neilvn.com/tangents/