I would like to grant minimal SQL permissions to some users who will regularly need to run 'static' reports - that is, reports on email traffic and on OWA and ActiveSync activity.
You will have to grant at least the following permissions to your users in SQL Server:
This will allow your users to run all "static" reports - i.e. based on data imports. The corresponding report categories are: Inventory, Traffic Statistics, Mailbox Traffic, OWA Activity, ActiveSync Activity, Server Traffic, Internal Message Delivery.