I take your ROM means the place as well? If so,
1) bouncing off the ceiling without a bounce card is going to be hazardous to your shots. The ceiling is equipped with lights, so bouncing off the lights up above will give your shots a light orange cast (since the walls are orange as well...) the bounce card will help to reflect the light softer and getting rid of shadows. Not to mention that the light is centered in the room, so at the table where the judge is, you will get quite dark shots on the judge's side, and the bride/bridegroom side tends to be brigther. The bouncecard should help in throwing the light to get a more even shot.
2) As recommended by some experts here before 75-80 is fine.
3) Yes, please do. You don't want the shots to turn out whitish. There's a bit of ambient light there, not a lot but can't say it's not enough as well. Capture it with a high ISO value of about 400
4) Might be dangerous, but the A priority would do fine, just worried that the camera might meter 1/15 shots for you. I think the last time I did ROM, my camera metered that
5) ARggh!!! no swivel???? Guess the best thing you can do is to ignore the fact you have a flash there, just tilt to the side and shoot, from the side your shots shouldn't cast a heavy shadow on the walls since your bounce card is still attached at 75-80.
Guys, if I'm wrong, correct me, thanks.