Which extensions can help?

[eluser]Animas[/eluser]
I am planning to create a auto classifieds system. I will use CI 1.6.3.

Common features:
1. User can register and login.
2. User can CREATE multiple classifieds ads.
3. Each ad will have multiple images and fields.
4. Users can EDIT their own ads only.
5. Visitors can search ads.

I need your suggestions on what available CI/3rdparty tools(library, helper etc) can be used here to ease my development(beginner).

What tools you guys use most?