> So if I've got this right, gain stage, get level mix, then start turning on the Master Bus stuff before getting to work on the details of the mix.
Yep, except gain staging is what you do as you add/active your channel plugins (and your master buss plugins too). The idea is you should be able to activate/deactivate your plugins without a perceived volume change, so in reality you're doing this as you go through the mix.
To make it easy to check if you have a positive change or just a change. If you boost the level changes may just sound louder, not better, but trick you with the volume boost. And to keep your levels under control.
Warren tends to be pretty loose on gain staging - you'll often see him using the trim of a plugin to boost level. The only other tip is it can help to normalise all you raw tracks first to get good level going into your chains (either dBFS or VU), beyond that it's using trims to bring volume up or down as needed. Richard Furch's tutorial on ProMix Academy has some a good section on what he does (he's a stickler for it. And it's a good pop-mixing tutorial in general, and has a section on normalising!). I'd recommend it if you can afford it.
> I've got the L1 set up threshold around 5.5 and ceiling -.2 or 3. It's bringing up the quiet but only stomps on a couple of loud moments in the choruses, so nothing drastic.
This is a reasonable amount of limiting for mix. I usually use a unity gain limiter at -0.2 to stop overs, but I'm mixing 3+dB hotter, so horses for courses.
> Oh, and James! Thank you again for the 3dB tilt clue. Bumped the bass up to 1.6. Life is going much better now.
Nice. Good to know that worked.
 over a whole mix this isn't really going to work, but should for a single channel, and definitely for a single effect.