Gain staging in hybrid setup

Hey Jon! Just curious, and might be a newb question. Do you have any tips when starting a mix in the box and what level of tracks do you like to use when gain staging? Is -18-ish really best when starting a mix and paying attention to keep it around there as you add inserts in the chain? And, after a mix before heading to the mastering stage, would it be advisable to keep the headroom in that same area before sending to mastering outboard gear, like the Xmaxx etc.? Just wondering what you find works.