@Christoph-M thank you for your suggestions!
Internet access control will be available as a commercial addon later this year and availably to subscribers for free. We expect both Veyon 4.2 and the addons to be available before summer holidays so deploying it during the summer holidays should be possible.
Limited file transfer support (only uni-directional from teacher to students) will be available in Veyon 4.2 but it initially will lack configuration possibilities.