I believe= 1 is crank.............2=house...............1+2 crank and house.
If anchored for a awhile ..put only on 2 so not to wear out your crank battery.
Yep. House batteries while not on shore power. That way you can always start your engines. I do not bother to switch if I am just out for the day and motor around every so often. But if I am going to sit beached or at anchor and run the stereo and other draining things, then I will switch to house only.