Microsoft licensing confuses everybody.
This borders on a legal question, and I want to preface this answer with the suggestion to talk to your authorized Microsoft reseller to get the proper answer for your specific environment.
However, to answer your two questions:
1) VDA is required for EVERY device that will be accessing the VDI environment, unless it is already running a licensed version of Windows covered by software assurance. The VDA licensing gives you the Windows OS use right for thin clients. The VLK activated virtual machines mean nothing and do not grant thin clients the right to access the system.
https://download.microsoft.com/download/1/1/4/114A45DD-A1F7-4910-81FD-6CAF401077D0/Microsoft%20VDI%20and%20VDA%20FAQ%20v3%200.pdf
2) Yes. In an RDS environment, you will require a user/device CAL for Windows Server AND Remote Desktop services for each user/device connecting to the system.
Just to clarify our terms, RDS is not VDI. They are two distinct technologies. RDS allows multiple users to login to a single server operating system. VDI allows multiple users to login to many available virtualized workstation OSes.
Again, even the experts can't figure out what Microsoft is doing from one day to the next. So, speak to your sales rep before doing anything.
