[nst7]

Generally, with analog summing, you want to split up your tracks fairly evenly. So using 14 channels, that's 7 stereo pairs. So if you have 30 tracks, that averages out to about 4-5 tracks per stereo pair. It's also recommended to put stuff in similar frequency ranges through different pairs. Like don't have the bass guitar going out of the same pair as the kick, or don't have cymbals going out the same pair as a tambourine, etc. With the 2 bus, you also have the option of using some channels as mono. It's typical to have the kick, snare, bass guitar, and lead vocal going to the mono channels, because they're all panned to the center anyway.

For coming back into Protools, there's no need for an aux track. Just set up a stereo audio track, with the inputs set to 3-4, and the outputs to whichever outputs go to your monitoring. You can set up a master fader as well.

The only reason to come back into Protools to an aux track is if you want to put processing on the master buss and record it that way (i.e., master buss compressor, EQ, etc.). If you want to do that, you would create an aux track with the inputs set to 3-4, and the outputs set to a stereo buss (i.e. bus 24-25, etc.). Then that buss would be the input of the stereo audio track that you will also create and record to.

On the Dangerous website, they have some diagrams that might help you.