I want to use a Windows Server 2016 instance as a Hyper-V host. This server should provide several Windows 10 VMs to users which connect via RDP onto the machines. Is this only possible with a RDS role configured on the server? And do I need a CAL for each connecting user (or respectively device) to be correctly licensed? Thank your for your answer.
With Server 2016 as Hyper-V host you have additional right to license 2 VMs per license running Server 2016 if you have Standard and unlimited VMs per license if you are running Datacenter edition. If you put Windows 10 in VM you must license it separately. Other thing is, Windows 10 is client OS meaning it can't be part of RDS farm. From what we have from information here, ii suggest you to use Windows Server 2016 as Hyper-V host, create needed VMs with Server 2016 image eliminating Windows 10 licensing, deploy farm and add CAL licenses depending on number of users/devices you have. Regarding licensing, you must license either each user or device you access RDS farm from.
BTW, you can make something like workaround scenario where you have VM running RDS roles except session host and edit policy to allow connection to your Windows 10 machine through RDP gateway, but again, in that case your Windows 10 machines are still not part of farm, so management and licensing for those machines are separated.