Will you be allowed to use a camera during the ceremony?
Indeed. #1 bear has checked and confirmed this already. They would prefer people not to use flash.
Just to help others to help you and avoid confusion......
Can you confirm that your camera uses an APS-C format, meaning a 50mm lens on your camera behaves more like a 75mm on "full frame"?
Maybe you could hire a top quality fast zoom that would provide most of the advantages of primes without having to change lenses? One would be horrendously expensive to buy, but when hiring...
I would need a v high quality lens with a range of say 50-200 and being very fast at the high end. I will need the high end in the ceremony where it is likely that I will be too far away for flash to be really effective, and in any case, they would prefer no flash photography. I don't want to lose image quality too much by bumping up the iso.
To be honest, I would be happy to compromise with one mid range tele for a nice sharp shot or three iduring the ceremony, then use my nice Sigma 17-70 afterwards when light and subject will be more 'controllable!