Indeed, timing is crucial. I would recommend to wait for an approval before talking about the salary. Salary is a sensitive and topic and important part of the negotiation.

The most important part of preparing yourself is imagining yourself working over there according to the information you have at that moment. Talk about the things that are still not clear or where you have your doubts. Than the questions automatically will fall onto its place.

Prepare for the job not for a list of questions...