we do not use the platform to post sheets but would like to - how do you control what seets are being posted? what if i have additions to the sheets that are to be included in the set?

You will need to create and publish a set. In Revit Ribbon interface under the Collaborate tab Click on Publish Settings > Create a new set > select the sheets and/or views to publish. Save and close. From BIM 360 create a new package to publish. Include the BIM model and the Sheet/view set you created in Revit. Save the package and publish it. You can add or remove sheets by updating the set under Publish Settings. Hope it helps

Under the Collaborate tab you will find Publish Settings, you can select what gets uploaded here. After selecting views/sheets to publish, you save and close. Then, still under Collaborate tab select Manage Cloud Models and you can publish your model and selected sheets to the cloud.

The Library section in BIM360 is used for uploading project documentation.