Multiple registration phases
Seems to me that you should consider the Profile2 module for getting this to work.

Excerpt from issue # 1796856 :


  Multi-Step Registration module works out of the box with Profile2 and all we need to do is assign the profile type to a particular step.


That same issue also contains some extra details about getting around possible access errors.

Refer to the Community documentation of Profile2 for more details about this module.