Off road whees/tyres

[The Mekon]

Currently have a Is250 for my wife and I drive a beat up old 1999 Prado.   Looking at scrapping the Prado (its that bad) and buying a Lexus RX350 2007-2010 model depending on what is around.  But I want to take this car off road at times and may need traction beyond what the standard wheel/tyre combination offers.  So what choices are there?   I am thinking steel wheels from a RAV4 16x6.5 with 215/70 dual purpose tyres.   Will the brakes fit inside these wheels?   Has anyone here ever done a down size wheel conversion?   Plenty of people wanting to do 19" and 20" wheels but I want the other way!