Little wheel help

My knowledge on what fits and what doesnt is limited.. Hopeing some of you guys can help me out..

I've got a 04 Cobra IRS rear, stock brake size.. I also plan on running the same brake size up front that came on a 04 Cobra... I have no clue what sizes they are LOL... I've been out of the Mustang loop for a long time..

So with that, do I need to run 17's? Or can I get by with 16's? I'd rather run 16's if I can... And, anybody have a clue what is the widest tire I can run on the rear with the IRS in a fox body? And what backspacing I will need?

I've done alot of looking, but havnt really found any info on wheel and tire specs on a swap like this.. Otherwise I wouldnt be posting :D