Vienta head unit are a piece of ***** i used to be an auto tech and i have done my own and they are easy. to answer the 1st q.. your immobiliser shouldnt be bothered by the new deck the security is just the head units security code. 2nd q.. soldering is always the best way it save **** coming undone and unexplained flicking on and off of the deck speakers ect... 3rd q.. all named brand head units are the same dimentions e.g. sony, pioneer, kenwood all that stuff and on the side of the decks there is useually either a T or an N (ie: toyota and nissan) for the bracets to screw into so ther should fit first time every time. Need anymore help i can get what colours the wires you need and all that for ya. im looking for the wire colours if you could still get them that would be great