How to customize registration process in Drupal 7?
You can create three roles named:


Personal
Business
Organization


Now you can use profile2 Registration Path module. This module will give you three separate profile for each roles. You can add separate fields for each profile. And from the configuration of profile pages you can enable separate registration path also.

Thus you can have three registration path for three roles and three registration forms also.

Now to create multistep form for profile2 module you can follow this question from this site.