A question for all my friends

...Or rather some questions... or maybe it's just one; I don't know, I'm tired.
Anyways,
At a job interview, How do you ask questions that could seem nosey, presumptuous or make you look lazy, ungrateful, etc.? I'm not nosy presumptuous ungrateful or lazy but there are some things that I would like to be able to get a feel for before I start working at a place. There are certain things that are very important to me in a job (particularly social services jobs) mostly because I know what i need to stay safe and sane and I want to know that I will be able to do so at the job I'm potentially going to be doing.
The questions are things like:
What do you do if a worker is on vacation and their case explodes?
(a place I used to work for before called one of their workers back from vacation because there was a problem with her case)
What is your feeling about a worker's recreation time?
(As noted above, some places care more about getting things done than their workers' sanity)
What is your on call policy (how do I discuss this one without sounding like I am unwilling or would be unhappy with on-call time?)
How do you help or encourage workers to prevent burnout? (I thought this one might actually be okay the way it's worded, but I wasn't sure)
What is your standard caseload and what do you do if more cases come in? (again not necessarily a bad question, but could make you sound lazy especially if asked in conjunction with a lot of the other questions above)

Also, what are some good questions to ask interviewers when they say "do you have any questions?"

And how do you answer stupid questions like "why should I hire you?" and "name three strengths and weaknesses" and... well i don't know all the stupid questions you get asked at interviews (you tend to get more "stupid" questions at business oriented places than social services, but I'll probably be interviewing for both to start with).