If the R-4 is like the R-44 you have to keep your eyes on both sets of meters... It is critical not to bake the pre-amp stage since you can look fine on the big meters but toast the signal before it got there... You don't want any clipping in the pre-amp (small meter) stage, which is really sort of an idiot light reading, so I set it at the level I can run the larger fine dial all the way up and not be clipping the big meter. By default that means the pre-amp stage is not clipping. Ultimately I aim to wind up no higher than -3 on the big meters (though usually it's -6 or lower since the pre-amp moves in 6 db increments). If you have to turn the fine adjustment down below 3/4 of the max you're likely to be clipping in the pre-amp.
0 is really 0. I'm OK with the peak anywhere between -12 and 0 (though hope for -6). Most of what I record is very quiet and very dynamic so there's always an adjustment in post.