Ok guys I have a avh-p4300dvd pioneer radio (double din). My question is at that back of that radio plate this is this chunk of plastic and metal bracket for more support what do i do to this? Do i just cut it out cause otherwise the radio won't go in all the way

 

That's pretty much what most of us do/have done. Even a single DIN has trouble fitting without removing the piece.

 

Do I need to cut the whole plate out

 

Just cut the plastic vertical part standing up at the back edge of the base plate and bend back the vertical metal tab behind it.