You're likely to get several opinions on this, so take mine as just that....one opinion
Do you really need all that routing trickery to get a good mix? I understand that some mixers swear by this method, but many of them are mixing stuff they did not record, so they have developed a method that covers a huge array of circumstances, while you are dealing with your own tracks. With that in mind, I think you could simplify(sometimes the best thing to do
) and get a good mix going to L&R. I would(and do) add parallel compression to drums with 1 stereo AUX, but that's usually all I do for "extra routing".
Moving to the final mix, I understand the appeal of routing thru a mix bus before the master, but(the big BUT), that is usually tied to trying to MIX and MASTER at the same time, which is not something I like to do. I will do "quick and dirty" mastering for a reference mix, but my final is usually done with the plan that I want the best MIX I can make(and leave the MASTERING for later, or better yet, for a real mastering engineer). When I do need to master my own mixes, I find I get better results if I make the best mixes I can and bounce those out at the session's sample rate and bit depth. Then I import all mixes for a project(assuming an album/CD) into a mastering session and then I can easily work all the songs against each other(which tends to make for better consistency anyway). I do believe in routing thru a MIX aux track, applying mastering plugins there because that processing happens before the master track/fader(master track plugins are all post-fader, so a fadeout can result in inconsistent limiter action).
Re the idea of multiple limiters, I agree and usually run 2(3 if the 2-mix is really soft). As with all this stuff, YMMV
