4. The sharepoint homepage takes a very long time to load (loading images, html title etc)
Most likely there is a Authzn delay happening for the image , png , cs , js files which can be overcome by excluding them from auth scheme . You can check the oam diag logs to check the time when authzn has happened and from them on what all policies are being evaluated for the items which can be excluded till the point when the portal loads completely.
Along with that from browser developer console, you can get the specific entities which are taking time .
In addition to Srinath's suggestion , you can play with some of the webgate cache elements. ( https://docs.oracle.com/cd/E28280_01/admin.1111/e15478/agents.htm#AIAAG5860 )
Especially try authorizationResultCacheTimeout when you see too much backend calls being made and delays being observed.