First Time Wedding Photographer Lighting Question?

Hi, I'm shooting my first wedding in may. I'm preparing as much as possible. One of my main concerns is the lighting within the church and reception hall. I'm going there today to scope out the lighting. However, I was wondering what type of flash I should use. I purchased a sunpak flash for my canon rebel. Should I also buy a flash diffuser for it? and also I wanted to know if using a flash ring is a good idea. Thanks.