Working with large number of users

I have an on-prem application based on OTMS that we're considering moving to Rainbow. Having played around a bit with the NodeJs SDK and seeing how long it takes until you're ready to execute any commands (and seeing what kind of data it goes to fetch, etc.), and having read about the 200 user limit, I'm wondering if it's the right platform.

The application I have in mind would monitor presence of around 3500 users, and it would need to set presence of about 300 users (those 300 users would be system managed users - no person will ever log in with these accounts, they are used only for my application).

Seeing as you can't do third party presence setting, you'd have to have 300 XMPP sessions (and I guess using the C# SDK given that the Node.js SDK doesn't scale - or even reverse engineer what the C# SDK does and do the things I need done myself), and I would have to add 3500 contact to the contact list of the user of my application (ideally without all these users having to add my application user to their contact list).

So.. does this sound feasible at all?