Which version of Java are you using ?  Could you please share your error log file ?

I think that will recreate the mongo collection index and not the OAK index. I am just guessing this but you can give it a try. Just rename the index folder under /crx-quickstart/repository folder and restart AEM. 

You can do it by updating the reindex property to true of index definition nodes under /oak:index. Are you able to access /crx/explorer or /crx/de UIs after restart ?  

I think you need to rebuild the OAK indexes as it seems they are corrupt. 

From the logs it seems the error is thrown when a particular blob file is not found. It could be that the file was deleted erroneously or it does not exist. You can try the following steps for recovery but I would recommend you to contact Adobe daycare support team for analyzing the root cause and p...

Can you check whether the AEM process has read/write privileges on datastore folder and can you share the exception stack trace/log file ?  

Did you start your AEM instance with the following run modes - -r crx3,crx3mongo for MongoMKCan you share the contents of following config files in crx-quickstart/install folder? Also ensure that there are no spaces in the paths of your aem installation folder. -org.apache.jackrabbit.oak.plugins.seg...

If you are on CQ 5.6.1 or later version then you can refer to the following code example- https://github.com/Adobe-Consulting-Services/acs-aem-samples/blob/master/bundle/src/main/java/com/adobe/acs/samples/schedulers/impl/ClusterAwareScheduler.java And for versions < 5.6.1 , you need to implement th...

I don't know whether there is any OOTB configuration to limit the file types. But there is a community article for restricting the upload based on size of the file - http://experience-aem.blogspot.com/2014/12/aem-6-sp1-classic-ui-restrict-large-or-small-files-upload.html. You can customize it and ad...

You can create a package with empty contents under dam path you want too delete. And then install the package to delete everything. Otherwise you can try deleting using the curl command -  curl -X DELETE http://localhost:4502/path/to/node -u admin:admin