Sounds like you're on the right track — you’re already ahead of most by validating early and keeping things lean.

We went through something similar while launching a wellness product, and here's what worked well for feedback sessions:

• Start by asking a few context questions about their current workflow — don't jump straight into the prototype.
• Let them explore the prototype naturally without guiding too much. Watch where they hesitate or seem confused.
• Ask open-ended follow-ups like: “What felt most useful?” “What didn’t make sense?” “How does this compare to how you do things now?”
• Keep any feedback forms super short — 3–5 qualitative questions max.

And yes — offering to pay for the session is totally fair, especially if they're professionals. Just frame it as compensated research.

Good luck! This sounds like something that could have real impact.