How many questions should I ask?
Two or three is usually right. If time is short, ask one strong question. If the interviewer seems happy to talk, a fourth is fine. Watch the clock and respect their schedule.
Is it okay to say I have no questions?
It is better to ask at least one. If everything was covered, say so and ask a broader question, such as what the interviewer enjoys most about the team. Saying no questions can sound like low interest.
When can I ask about salary and benefits?
Usually with HR or the recruiter, or once there is an offer. If the interviewer brings it up earlier, it is fine to discuss it then. Have a researched range ready either way.
Can I ask about next steps?
Yes. Asking about the timeline and next steps is reasonable at the end of any round, and it helps you plan your follow up. It also tells you when a polite check in would be appropriate.
Should I write my questions down?
Yes. Bringing a short list, on paper or on screen, shows preparation. Just make sure you listen and adjust instead of reading them mechanically. Cross off any that were already answered.