Let me please share some further details for the Test Studio and Telerik productsand licensing, and hopefully this will help you sort out if you need to purchase anything in addition.
Test Studio Ultimate
- this version includes Test Studio Standalone, Test Studio Mobile, Test Studio for APIs, Test Studio Dev Edition (which is basically the Visual Studio plugin), Load and Performance modules.
Test Studio Web&Desktop
- Test Studio Standalone, Test Studio Dev Edition (a.k.a. the Visual Studio plugin)
Test Studio Dev Edition
- the Visual Studio plugin can be also installed on its own as part of the DevCraft Ultimate product bundle.
Though, all of these products do use a per machine licensing which can be swapped between different machines as described here for Test Studio Standalone
and here for the Test Studio Dev Edition
So, as far as I understand you do not need to buy additional licenses if you already have an Ultimate one.
I hope this will be helpful for you.