Sources
Billing is the only required source. What each source turns on, and what stays unavailable without it, is on Connect your tools.
Refresh
A source connects by the highest method available to it. The method determines refresh.
Every screen states the freshness of the source behind it. A weekly export is never presented as a live figure.
Where a row reads set per connection, no single method applies to every customer running that source. The method and its refresh are agreed and stated before the connection is made, and appear on the screens that depend on it. No interval is published here that would not hold for the system you run.