I would always sugest C# for writing Tools as you dont need the power (and costs) of C++ for this. Framerates may also not be the problem in an animation tool. Also image/texture support is better using C# vs. C++ PNG libs.
You could use OpenTK for that, the OpenGL part should fit your needs where I agree to sirpalee for not using Vulkan at this topic, it is to heavy for that. You would work at least a couple of Weaks just for getting Vulkan environment 'as general' as you need it in your tool so switching to the lower learning curve of OpenGL would be the best choice here.
You simply should learn how to initialize Textures and create your Meshes via Framebuffer that should be enougth because OpenTK handles anything else from getting the Window ready to handling various kinds of Input and calculating the Math needed to upload anything to your shader.
Google for UI Tutorials, it isnt that heavy for simple ones or you create the GL context for a .Net panel and render in that and use Winforms for your UI. I made that a couple of times and it works very well because the Winform Controls can get a pointer to the handle that will be passed to context creation of GL create a render-ready context as well as using a window for that