For every user with access to the Q&A module, also give them Q&A Email rights. That way, all Q&A users will receive email notifications when they are responsible for taking an action.
If multiple organisations may need to ask questions, set up the site as a
Bidder site.
If the site is not set up as a bidder site, do not give a user who is part of a bidder organisation Reply or View-All-Questions rights.
For commonly occurring questions, the Site Administrator, or a user from the selling organisation, can ask a question, answer that question themselves, and then disclose that question to all other parties. This is similar to creating a FAQ.
If a question is going to be disclosed to other organisations, make sure there is no identifying or confidential information in the question or its response(s). If the question is not "clean," using the technique from Best Practice #4, the Site Administrator can simply recreate the question, remove any identifying information, and then disclose the recreated question.