HiI already implemented comment function in AEM 6.1 with MongoDB. You have to configure the storage configuration for author and publish instance. They need the common configuration, otherwise the comments (UGC) will not be replicated. You can inerhit the most of the functionality from the default c...

HiI tested recently Apachae Solr 4.9.1 with AEM 6.1 and it works without any problem. I did not have any problem with that version.To your second question I have no answer, I am sorry. To the third question, I think it depeneds for what you want to use Solr. I know that AEM 6.1 has a integrated Solr...