Appropriate Wheel Offset for 18" Wheels?

Picture 1: IIRC, the wheels may be 17 x 9 as the tires bulge out a bit. So, I threw almost 100 lbs in the trunk and added about 0.200" (5mm) as the suspension wasn't loaded enough. Leaf springs look almost flat now... Picture 2: About 3/4" from tire to outer trim. Picture 3: About 1/2" from tire to leaf springs.