Application Number of Users

Unfortunately this is a bit of a difficult question to answer without knowing more about what the application does and how it's architected. For example, a forum like this one could absolutely support 100K users on Remy with no sweat. A simple marketing site can easily support millions. But if you're trying to build something with 100K users who are each doing something like uploading movies, for example, you will likely start to run into service limits and quotas that will need to be addressed.