Infrastructure specs for very heavy loads

Greetings everyone!
The organization I work for would like to set up a videoconferencing environment in order to replace the commercial SaaS service it currently relies upon.

There are currently some 300 registered users, whose use cases span from simple 1-to-1 meetings to training sessions including medium groups, up to large events hosting hundreds of guests.

Based on the stats provided by the current platform, the average number of simultaneous users engaged in a call is between 100 and 200, with around 25 cases in a 2-years-timespan in which the concurrent users count went over 300 (with one case reaching 600, three cases reaching 700 and one peaking at 821).

Based on your experience, could you give me an idea about how many servers (in terms of HAProxies, Jitsi servers and Videobridges) we should deploy in order to meet those requirements?

Thank you very much in advance!
Best regards
Bruno