A clean SQL Server maintenance plan should include three processes, backup, integrity check and index optimize.
You could simply set up a SQL Server maintenance plan within the SQL Server management studio. But be aware that there are better solutions, E.g. Ola Hallengren’s SQL Server Maintenance Solution is my absolutely favourite.
As many other Windows services SharePoint and SQL Server requires different service accounts in order to run secure and reliable.
There are different concepts and strategies to create service accounts for a SharePoint installation. One of the most reliable solution I’ve found here.
It could happen that the directory sync service (DirSync) doesn’t sync the users UserPrincipalName correctly.
I had an issue where the UserPrincipalName from a user in the Office 365 windows azure directory has been made based on the user’s sAMAccountname. This wouldn’t be problem if as long the sAMAccountname is the as same as the UserPrincipalName, but as you can guess this is not everywhere the case.