Dhackworth

You will need to keep in mind that with ICF's wall openings are framed with pressure treated 2x's. These serve as a concrete stop as well as a surface to attach the windows and doors to. Your openings will have to be 3" larger than the rough opening specified by the window / door manufacturer. With all of that being said I would make the ICF's a minimum of 12". This will also allow a bit of room to get your rebar installed and maintain 3" concrete coverage over the bars.