Create a log module with a log() function that other modules can call.
This will require creating a new table with the following columns:
What types of events should be logged?
Suggestions for events to be logged:
add or delete user
change user permissions
add, delete or change plans
add, delete or change roles
The hope is that we could roll back erroneous changes, or at least know who was responsible.
add to that list add, edit, or delete payments
(it's tempting to just write LOG ALL THE THINGS, but that would get a bit big :P )
I'd like to take a crack at making this module. It would be a great paper trail or audit trail for others to ask "Hey who added this credit to this member's account?" and get an answer! Would this just be like any other module / add on or would there be something different?
This could be a very simple module to write. I'd suggest modeling it after the drupal watchog module: https://www.drupal.org/node/86124
You'll need to create a database table (see how other modules do it).