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#11
Yes, 2.68GB is the size of the total download to upgrade you to the next version. It will be downloaded in smaller chunks.
The features updates work a little differently from cumulative updates. A cumulative downloads a few patches and replaces on or two system files. If a restart is required it will be scheduled for the next time you reboot.
A features update upgrades you to the next release of Windows 10 and replaces the whole OS, keeping your original one in a windows.old folder in case you need to roll back. To do a full upgrade it has to download the install files for a whole new version. This happens in the background and may take some time to complete. You can use the PC as normal while this is being downloaded.
When completed, you won't be forced to install at the next boot. You will be able to postpone it until a time that suits you. The upgrade process can take anything upwards of an hour (and in a few rare cases, a lot longer, so be prepared to leave it running over night).
Note that the upgrade will want to check for updates during install. As you have already downloaded the Standalone installer for the latest 1709 cumulative update you do not need to let it do this. Just make sure you keep that update handy so you can use it after Fall Creators update has installed.