In my iPhone 6 iTunes and App stores there is automatic downloads in which my Updates are on. Can I keep these Updates on or shall I turn off to prevent mobile data usage on roaming, or will these updates only happen on Wifi?
You can also turn Automatic Downloads on or off over your cellular network on an iPhone or iPad Wi-Fi + Cellular. Go to Settings > [your name] > iTunes & App Store and turn Use Cellular Data on or off. Cellular Data downloads are limited to a file size of 150 MB or smaller.