The WD My Cloud User Manual (http://www.wdc.com/wdproducts/library/UM/ENG/4779-705103.pdf) explains how to setup and configure the My Cloud to accomplish most if not all of those actions.
Because the WD My Cloud is a network attached storage device it can be used as a storage location for any backup software (like the included WD Smartware).
Once you activate the Remote Access features of the WD My Cloud and configure a User account for remote access within the My Cloud one can use the WD My Cloud Desktop program, the Android/iOS mobile apps, the MyCloud.com website to access your My Cloud contents while away from home.
You can copy any of your media content to the My Cloud, and so long as its in a Share/Folder with Media Serving activated your Roku, using a free channel like the Roku Media Player, will be able to stream media content from the My Cloud.
The WD My Cloud includes a backup feature called Safepoints that allows one to backup the WD My Cloud to either a external USB storage device connected to the My Cloud’s USB port, or to an external network storage location on another computer or network attached storage device.
Again, the User Manual explains how to do many of these tasks, from setting up new users, new shares, activating media serving on those shares, how to use Safepoint, how to use Smartware, and how to use many other features and options of the My Cloud. There is also some basic help information located at the MyCloud.com under Helpful Topics: http://www.mycloud.com/learn/?id=mycloud