Lets begin with the basics. The Essentials for Office 365 solution should be installed in a location where computer resources are abundant and you have full local admin permissions to install, configure, schedule and execute operations. If you are planning to store your backups on a local or network file share be sure to have both read and write permissions to this location and if you are choosing the cloud option, make sure to have full read and write permissions to your Azure or Amazon storage account. And of course, you will need the appropriate permissions in Office 365 to be able to connect, backup and restore to the various services. To keep permissions simple, please have the following:
•For SharePoint Online, you will need to have Site Collection Administrator permissions for every site or site collection you wish to backup
•For OneDrive for Business, you will need to have Global Administrator to your tenant For Exchange Online, you will need to have Global Administrator to your tenant.
When it comes to planning, you will need to decide what is mission or business critical and therefore needs to be backed up. I know the easy method is to select the Include All option, but with that comes caveats. Most apparent is that the more you include the longer the back will take to complete and the more storage space it will consume, so before you click that option decide if it is business critical to use this option. Content from Office 365 takes time to extract and the more backups that are running concurrently the resource consumption that will take place.
NOTE: If you have not already, please consider reading the Essentials for Office 365 Performance Optimization Guide for a deeper understanding of resource consumption and optimal configuration of the solution.
As a simple example, imagine you want to create an OneDrive for Business backup for 500 users and each user has an average of 25GB of content in their Documents library. That means you are creating a backup project that will initially contain over 12.5TB (terabytes) of content. Extracting or downloading that amount of content from Office 365 or any online location will take a considerable amount of time, not measured in hours or days, but rather in weeks. Please plan accordingly based on what is considered mission or business critical content.