I don’t think a single Ignition server can handle 3000 clients concurrently. I believe we have only tested for around 150 concurrent clients.
What will that Ignition server be doing? Realtime status and control? Historical trending? How many tags?
I bet you could get around 500 clients open at the same time which means you might need to have 6-10 Ignition servers for that load. We would have to setup a stress test to see exactly how many clients can be opened according to what you want the project to do.