Hi Natacha,
If you go over the participant count for your subscription level, it would be good if you could make extra contributions via Open Collective - as per our fair use policy 
But your subscription level should not effect audio. As more participants join it becomes even more important to mute when not speaking and to use headphones… and harder to ensure everyobe has suitable connections speeds. For more about audio and what we are doing to solve any issues please see this thread Audio Issues with BBB
All the best
Oli