Optimal db for tracks

Hi
I’ve asked for that too without having a proper answer.
In my case, I first tried to export at -0,02dB but I noticed some clipping on bass files so I decided to try to export each track at -3dB (I put a dynamic plugin on master track on Cubase,).

But then I still didn’t get how to manage the mix, I’m on mac and uTool doesn’t work very well. I’m waiting for the new v2 that should solve problems.