IT is reviewing this. Will update back once this is fixed.

No, you can't use Datastore GC using Oak-run tool.Although you can use curl command to invoke the Datastore GC  from the Jmx mbean exposed from your command line. See (1)(1) : Data Store Garbage Collection

All folders you see in /misadmin are under /etc so you can just navigate to msm/rolloutconfigs and create your own configs

For AEM 6.2, You need to install FP-17061 to get this functionality. Open a daycare ticket to get access to it.

This is already fixed in latest maintenance releases. Please update the instance to latest Service pack and CFP and this should be taken care of.Download the CFP and SP from Adobe Experience Manager Help | Release Notes: AEM 6.3 Cumulative Fix Pack

Go to useradmin, For everyone group make sure you have read permissions to /etc/tags and folder under it.In AEM 6.4, the path for the tags would be /content/cq:tags. You can check for the same permission for the everyone group.

my 2 cents : I understand what you are trying to do here but don't think it is possible OOTB. IMO concept of  CF relies on the content structure which inturn relies on the referenced content(asset, text etc.) which later can be consumed internally or externally where all these assets reside at a cen...

AEM (only author instances) with MongoDB only supports replica-set architecture. Sharding is not supported.(1) : Recommended Deployments

You need to modify your index definition(say DamAssetLucene) to include an analyzer which would have a file which contains the stopwords. You can add all the metadata keywords in this file and after you reindex, fire the query you won't be able to query for such excluded keywords.More information on...

you can rely on prefetch section at (1) for prefetch of dispatcher cache(1) - Optimizing the Dispatcher cache