Need to b educated !

I have a 2011 Ford F-150 XLT 4X4 super cab 5.0 liter V8. Currently sporting OEM 17" 6 lug 5 spoke aluminum rims. Currently in the process of upgrading my wheel package to OEM FX4 6 lug 6 spoke black rims sporting 305/55/20" Micky Tompson ATZ's including a BDS 2.5" front lift & 1" rear. My question is......Must I also option in wheels spacers to honor this upgraded package? If spacers are required what will be considered a minimum spacer size thickness?