Hi Cyril,
no, there are no special rules for mixing sessions with specific track-counts. In bigger projects the engineer might be in charge for 150 and more tracks, so the most important aspect is to keep things neatly organized, colour-coded. Make sure that all individual tracks are carefully edited. Later-on it helps to think in terms layers and groups rather than in terms of single tracks, i.e. "depth" and "width" or "hi strings" and "low percussion" opposed to "reverb 1, room mic 3" or "close mic Vi1-1, close mic Vi1-2" and so on.
Good luck!