Giving a good speech can be difficult and stressful. Trust me, I speak in front of large crowds every single week and it isn't something you master quickly. I can tell you that after years of public speaking, it just comes naturally and I barely even think about it these days.
Standing in front of a room full of people, with a photographer and videographer can be very intimidating. Don't let get to you. In fact, don't even look at them! Look past them at various things around the room. If there are lighting fixtures on the wall, look at those and focus on what you're saying and say it clearly.
As for writing your speech, what to include or not include... take a look at this article from Brides magazine: