Hi Shake, -6 dB is too loud imho. It’s all about the headroom you need at the master output. There is no real reason to work at -6dB as opposed to -12dB. I work at -12dB on channels, some people work at -18dB even. Noise floor is not a problem as long as you record your hardware and mic at 24bit. The theoretical noise floor at 24bit is -144dB. So that would mean you’d have to listen at ear-deafening levels to hear noise in your recordings caused by that noise floor. It’s the reason why we have 24bit.
Regarding commercial standards: iZotope has this all build in since it’s a mastering suite, but this is why we use a limiter. You’ll boost the volume at the last stage inside iZotope when using the limiter. Usually I’ll set the ceiling to -0.3 or -1 dB and then start adjusting the limiter accordingly. Inside iZotope you can also boost the input gain to get it to a level that makes it easier to work within iZotope and its meters.
So to summarize: You simply bring back the levels to “0” at the last stage when your track is done.
The easiest way to manage this gain staging is to create a template and put a utility / mix tool on each channel. When a you use a mix of hardware and VST’s you’ll notice that VST’s always start very loud. So unless you use presets that are reduced in level, it’s easier to simply set the mix tool at -12dB for that VST.
The opposite is true for using overdrives. You want the signal to go in pretty hot into the overdrive, so you might want to boost the volume of a mic recording that peaks at -12db with +10 dB before it goes into the overdrive VST. Then, if needed use another tool to bring the volume back after that.
Heh, this post become much longer then expected. Hope it helps. Cheers!