Need guidelines on reindexing learning after an update or a refresh

I've been getting a lot of mixed answers about the need to reindex and exactly what is required after each update or refresh.

• Do we have to reindex all of the learning indexes after each update and after each refresh?
• Do all the reindexing jobs have to run one at a time or can they run simultaneously?
• Is there a way to make the fa-hcm-learningrecord or any of the jobs run more quickly?
• Is it necessary to wait until all the indexing is complete to do validation testing and open the system back up for users?
• Are we able to run learning reindexing jobs at the same time as other HCM reindexing?