Purgatory is about purification, not punishment, so indeed the passage does not suggest that. However, man is likened to a building built of both noble and base material, and the base material burns off; the building is then freed of "the stubble", so in the analogy that St. Paul is giving us, the man who is the building is cleansed. The building materials are analogized to man's work, and some work is sinful. So that is sin that is burned off as stubble. Finally, the man is saved in the end of that process, so it does prepare him for heaven.
No! The building is the CHURCH, not the believer! And the ‘fire’ is a term that merely means the work will be made manifest - and it says so, in the text.