With a stabilizer reading of 42, you need to keep your cl level between 3-6ppm all the time and when you need shock, it will be 15ppm for this pool. So, each evening when you test, add however much bleach you need to take your cl back up to 6ppm. In a 5000 gallon pool, each quart of 6% bleach will raise the cl by about 3ppm.

When you go out of town, I would shock the pool ahead of time and then cover the pool, but maybe leave a corner open so it can vent after is has been shocked. Maybe leave the timer set to come on a couple of times each day and run for about 2 or 3 hours each time just to keep some circulation. If you friend can come mid-week and add another gallon of bleach that would be great. You can also add a dose of Polyquat 60% algaecide for some added insurance if you want. Make sure your pH isn't too low. Don't want it to drop below 7.0 before you return. (If your pool does get a little green, it will easily be cleaned up with some bleach, so don't worry too much.)

Hope this helps and have fun!
(Regarding pump time when you are using the pool --- I usually run mine for 8-10 hours per day.)