1. Yes plucg in an audio cable from their audio board to your camera. Most often it will be a line out feed that you’ll have to take as a line input into your camera. Don’t use Mic inputs. As others suggested, you’d be better off adding a wireless mic to the podium and plugging that directly into your camera. I would ONLY use the audio feed from the house audio board as a back-up. Put your wireless in Channel 1 and their feed in channel 2.
Please make ure you use good headphones to monitor your audio.
2. For B-roll get as much as you can of people listening to another speech. Smiling, laughing, writing notes, nodding, applauding, etc. Get variety…groups shots of listening, two shots, three shots, etc. etter to have these shots and not need them then to need them and not have them.
3. Every podium shoot is different. Change your framing by zooming in and out leave some headroom. Honestly, shooting an event like this is only for those who know what they are doing. It’s live TV…you can’t get the audience and speakers to come back again…you have one shot at getting this. if you can’t do it, back out now before it’s too late.