Newbie needs help for a new idea start

[eluser]earthdog[/eluser]
Hi All!

I have read in a signature here : "Every tool for a specific need" , or something related.

I need to build a site like http://www.penzu.com

-Central content creation happens with a tinyMCE editor saving the contents in a DB.
-But then i want to build custom businees logic on these data from db.

I will need encryption,auth,file management (for exporting) e.t.c.

I am new to PHP, never writen a full scale app in php, only small pages (coming gfrom .net winforms).

I am researching many days regarding which framework i could use. I could do it without a framework by just using PHP alone , but i want to dive into the world of PHP frameworks.

Proposals were fro CI as well for other frameworks that are written based on 5.3..Since i am a beginner i don't think that i will know these differences until some times passes

Codeigniter is my choice up to know but i do feel good about Yii too.

Respecting the saying "Every tool for a specific need", am i ok with CI?

Thanks
Elias