Too many variables for generalization: short-haul vs long-haul, night freight vs pax, legacy vs low-cost carrier...
Jumpseating is NEVER guaranteed! Plan on spending a day at it, until you figure out the specific routes and trends.
Check individual airlines for junior domiciles.
Some pilots are chatty, others not. Again, lots of variety.
Number of days off may not vary so much as distribution. You may fly 3 on/4 off, or 5 on/2 off, or 16 on/15 off, or any variety. Again, depends on airline, airplane, and seniority.