Backspacing matters for both looks and functionality. The smaller the backspacing, the further the wheel will stick out past the fender. While this can prevent rubbing of the UCA, it can make it easier for the tire to rub the bumper and pinch weld when turning.
The more backspacing, the closer in a wheel will sit. This can cause the tire to rub the UCA. There are a few that have successfully run a wheel with as little as 3.5' backspacing. There are also some that have run Tacoma wheels with 4 7/8" BS...although a wheel spacer would be helpful in that situation.
The perfect BS for the 3rd gen seems to be between 4"-4.5" when running a 285. While there are a few people running a 4" BS, it is more common to have 4.5". Many more wheels are made at 4.5". Take a look at this thread...there are some 4" BS with pics, as well as 3.5" and 4.5".
3rd gen Aftermarket wheel thread