Urgent ! Server requirements for 3-5 thousands participants meeting

Hello, we are planning to have a huge conference, the conference will be like the following:
1- just two users use Video (the rest of users will not be able to turn on their cameras)
2- active recording
3-screensharing just allowed for moderators (2 users)
so what is the server requirements (CPU, memory).


Let other participant watch stream through YouTube or custom rmtp channel.
We have a similar system which we use regularly.