With some EQ, dynamics, and imaging adjustments, mastering can fine-tune the blending of sounds within the entire song, but it won’t make any major volume level or sonic flavor adjustments to individual components. You don’t want to focus so much on trying to boost the overall song volume level when you are mixing as that is an aspect that would apply to the master output of the mix and, hence, should be left to the mastering engineer to handle for you. The only overall volume level issue you need to worry about during mixing is to make sure your levels are not clipping as it will cause digital distortion that cannot be repaired in mastering.
I typically send a follow up email about a week after the initial proposition and then I’ll call their office to follow up a week after that. This is why it’s good to get the ball rolling as soon as possible. Organizing events even months in advance is easier than cramming a ton of planning into just a few weeks.