Not necessary if she will file I-485 as your dependent, but she

I received A#, 
-You don't have a true A# until you file I-485.

 Does it mean I am about be approved? 
-irrelevant.

Can I use it to apply for home stead? 
-Don't understand what you mean.

how can I find out my wife's A# if possible?
-After she files I-485.

 Thank you for your answers