[Users] SER in production environment

Hello, We would like to use SER in a production environment and provide presence support to at least 5000 *online* users through a publicly available service. We are particularly worried about scalability. * How stable is the presence module? * Does it support RFC3857 to allow authorization management of subscriptions? * For such a big number of users, do we need several computers running SER? * If so, how can we ensure that all SER servers have the required information to be able to send status changes to all users? Is that stored in a MySQL DB and if so, how is it determined which SER server sends the NOTIFY on state changes to all users having the user whose state changed in their list? * Are there bandwidth estimations? I have the feeling that 5000 online users will generate many NOTIFY messages due to presence changes. * Is it possible to prevent MESSAGE requests to be sent following some piece of information found in the database? We would like to connect SER to a SMS service, and prevent users to send SMS'es when their credit is not enough. That supposes some computation in the ser.cfg file, is that possible? Greetings, Luba Vincent