Residency permit

I apply for my 3rd year marriage extenision soon. Upon the completion of the 3rd year to I apply for a 4th year extension

and aply seperatly for the residency permit.

1.What is the likely hood of recieving this permit?

2. what do i gain if i get it?

3. does my 3 year time with O type visa count at the beginning, or only after i received the marriage visa?

Thanks for the info