Well you should probably start by using the proper equipment for the audio system. Resi gear is not suitable for commercial installations, even though you can get it to work. You should use a 70v amp and plenum rated in-ceiling speakers. If you'd like, you can do a proper stereo speaker setup by the main front display for video sources.

Like Joe above says, you'll need to figure out all your ins and outs of the system for audio and video. For conferencing, you'll need a dsp that all audio runs through so that you can maintain proper gain control and have a good reference for AEC.

I find that projectors leave a lot to be desired as far as punch for these rooms. I'd prefer a video-wall where you can have one large image or split the screens up to show several images which is great for collaboration. I'm sure this client does a lot of that. For others along the stadium seating, install several larger displays as convenience/spill over that show what's on main display.

Should be enough to get you going in the right direction. Since it's your first, have you considered partnering with another firm that does this day in/out? You can certainly help with the labor and learn a lot while the job goes on.