I am not familiar with specific wheels you are looking at, but this won't change the general backspacing needed for your car. You might want to make sure the wheel/spoke design will fit your brakes, but you will probably be fine with stock brakes... I would recommend 6" backspace for the front 18X9" wheels. You could probably go as shallow as 5.75" and be fine. If you decide to go 11" on the rear, you will want 6.75" backspacing. If you go 10" on the rear, you can probably go anywhere between 6" and 5.75". The more shallow the backspacing, the more "flush" your wheels will be with the fender.
Here is a picture of my car with 18X9.5" fronts and 18X11" rears. Backspacing is 9.25" on the fronts, and 6.75" on the rears. This would be the same as your car with 18X9" (with 5.75" backspacing) and 18X10" (with 5.75" backspacing). Of course, if you 11" in the rear, you will want to stick to 6.75" backspace. This general configuration puts the wheels almost "flush" with the fender, doesn't interfer with the stock IRS at all, and doesn't rub the tires on the fender. I do have the fenders rolled though.