1) When you go to Access Point youre running the app at the server. So data consumes RAM on the server and only what is needed for visualization by the browser on the client.
2) User clicks in the UI and the server responds to this by applying app logic which affects the underlying data model which most often leads to recalculations and the UI is rendered partly on the server using advanced cache mechanisms and the result is sent back as graphics and HTML. So only the data that is needed for visualization is sent back to the client each time.
3) How much it will expand to in memory compared to the QVW depends on the data itself. It could become 2 to 4 times more in memory compared to the QVW on disk.
4) To have a margin I would say 3 to 4 times. For each concurrent user you can add ~10% overhead memory wise.
5) That is limited by your licenses, the amount of RAM and the number of CPUs and their speed and cores and lastly and very importantly how your application and it's data model has been built. And yes many users will bring down the speed and performance - it would defy the laws of physics otherwise. However QlikView scales extremely well and make very good use of the hardware.
6) There is AFAIK no way of limiting the number of users of a particular application.
