Adding own variables on user registration to created user
How about using the Profile 2 module for this? Exceerpt from its project page:


  Designed to be the successor of the core profile module, which is deprecated for Drupal 7. In contrast to the deprecated module this module provides a new, fieldable 'profile' entity ... leverage the power of fields!


Refer to this video for an introduction to Profile 2 also.

Maybe you also want to consider something like the answer to How to display a profile form using profile2 module ?