Figuring out FOV and Angle for a Reference? How to use a Reference Image? I want to start modeling a character from multiple references. The original references are just images of the character and are NOT standard references -  which means I should calculate the Angle of the camera, Fov etc. What should I do?

Another problem that I've had, is about references in general . I've been using background images to load references ever since I started working with Blender, because if I used images as planes it'd go invisible if I were to go to wireframe mode. But images as planes seem more comfy and easier to use. Is there a way to avoid this (to still being able to see the image when in wireframe mode)?
Images as Planes are textured plane geometry, so they can only be viewed in Texture, Material (LookDev), or Render mode.  Use the Empty/ImageType for your background image.  Select your camera view in the viewport. (numpad 0).  Then Add->Image->Background (in 2.8).   This will create the ImagePlane square to your camera view.  In the Properties -> Object Data choose the Back depth or Default Depth.  Just remember that you cannot render the background image in your final render, but you can render it in Viewport Render from the View menu.