How to gather information of users based on their role?

Hi,

I have build a Drupal based website where visitors can create accounts but administrator approval is required.
The administer assigns a role to the visitor. There are roles for teachers, PhD students, students etc.

Now, I would like to collect some specific information of the users for example of the PhD Students I would like to know the title of their Thesis.
Later on, I would like this information to show in a View.

What will be the right approach?

Using the profile module? Let the user when he 's creating his account select his role, and adding for each role in the registration form some extra fields. Is that possible?
Of course administrator approval is required. In that way the user can update his data later on.

Using the Web form module? Once the user has logged in, show a webform (depending on his role showing different fields), which the user can submit. In that way the user can submit his data more than once and that`s actually not what I would like. Or is it possible to submit the webform only once and not show it anymore later on?

Are there other options?

I hope someone could guide me into the right way.

thanks in advance.