If you have one camera springing for a prime at a wedding is not your best option when you dont have a speedlite. Get a speedlite 580 or better, extra batterys, at least a 32 gig card,extra battery and two stofen diffuser.One whiten and one amber for natural/warm reception shots that have tungsten lighting. Shoot raw, ISO 400 for posed shots(Stay away from strong lights that can throw off white balance), 1600 for reception/ceremony candids(good place to use amber diffuser), Maybe 3200 if you are good at exposure. Outdoor shots should be shot in shade with flash where possible, your diffuser wont help much here so direct flash is better here. The reason I say dont buy the prime is flexibility is your greatest asset here. Shoot f 5.6 for any shot that includes more than one person, It will be sharper and both people will be in focus. Good luck, have fun, Practice on a few people ahead of time!