Wheel Clarification

I have a 2009 Tacoma Base 4x4. I understand that my stock wheels are 16x7. I am in the process of buying some new tires, have the stock Dunlops on it now. Going up a size to 265-70-16. Most all the tires I look at say "approved rim width" 7.0"-9.0." Then it will say "measured rim" width 8.0." Now I realize the tire must have been tested on a 8.0" rim. My question is what difference would a 7.0", or 8.0", or 9.0" rim make? Also, what is the offset of the stock wheel? Does + offset mean it will stick out more or would - offset make the tire stick out more? Thanks men.