Some questions before choosing/start learning Yii framework

I've been developing simple PHP/MySQL web sites for some years.
Never used a PHP Framework before and I understand I'll need to know OOP, no problem.
I'm about to start a SaaS project of my own.

A)
So far, I've seen Yii generates the CRUD and pages according to the DB.
Is it easy to modify the generated code?, like, adding a new DB field and its form field without not generating again all the stuff every time I change something in the DB and losing other customizations?

I mean, I'm 100% sure the generated DB code and pages are not going to be enough and I'll be constantly adding and correcting fields, and adding more tables etc.

B )
My project will include a Shopping Cart and Calendar(for events, tasks, etc.).
Does Yii has these options or at least an easy way to implement it like the Authentication options or Database listing, etc.?

C) Does documentation has this explained as a tutorial/book or is more like a reference(minimum explanation that only advanced user understand how to integrate it)?

thank you very much

Answer

A) Yes, it's easy. You will just add code for new fields not changing it all.

B and C are answered by Stratosgear very well.