I am by no means an expert on that topic, but I would assume that while a big cloud instance could go far with regards to CPU and memory, network bandwidth/traf

I am by no means an expert on that topic, but I would assume that while a big cloud instance could go far with regards to CPU and memory, network bandwidth/traffic could quickly become an issue with several 1000 users. Depending on the amount of work you are willing to put into this, you could even start with a load-balanced setup were one or more web servers, jicofos and prosodys are distributing the load to several videobridges. That would make it easier to scale the system up by adding additional instances.