Yes, 64GB
Leave the Syn3 Updater in automatic mode. Change your setup to show your present Sync version as v2.2.16280, NAV APIM, EU region. Save that and then go to the upgrade screen and select the EU region, Sync 3.4.23188, and the EU maps. Start that and the Syn3 Updater should do it all and place the files on the USB. Once you select the options and start the download you do nothing until the USB is done. Then take it to the vehicle and with the vehicle running, insert the USB and wait for the installation to finish.
Here is an article that shows how this goes. See the Installation Instructions section.
Current EU Maps Installation on US Imported Vehicles - Ford / Guides - CyanLabs Official Community