I don't think they can "not allow" to ask questions, that would be weird, wouldn't it?
Some answers they will give you themselves, when telling you about the company or asking you questions. I.e., "would you be willing to work overtime?" certainly tells you something about the work-life balance.
I would ask as many as I could, it's in my interests. If them have strict timing, they'll typically give you contacts of a person to ask further questions, and you can email/call them with the rest.
Good luck with the search!
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