you’re losing a lot of resolution and bit depth by mixing/record/exporting with such low levels. When you boost the volume later you’re also boosting all the noise and because of the crappy bit depth your mix will sound terrible
there’s a bit on the Steinberg video I posted to you up there^where he talks about gain staging (around 10 minutes in I think) watch that a few times & take his tips about using a reference kick and a reference track
and ditch your master buss limiter until you’ve got a handle on the rest
that’s my advice