Offset and spacing question

Sup People, I'm getting my INTRO's (Ya! me) but my question is, since im changing over the front suspension to Toyota do i just order wheels that would be for a Toy? and how do i figure out correct offset for the Rear. its going to have a IRS, and i know there is a mathamatical way to figure it out. Thanks for your Help.they are 19"x8" Twisted Vista II's