MDX question

Answer 1

This is a classic slowly changing dimension issue. What you are describing is a type 2 slowly changing dimension see here

You need to make sure that your user dimension has a surrogate key. Then you create a new record in your user table each time the user changes status and then you use effective dates to control which surrogate key to insert into your fact table. This will let you report on the users effective status at any point in time.

Answer 2

I think you need a "User Status" dimension, then you can show this against Time, with the measure being count of users.