1: On Windows, OpenCL.lib is a static wrapper around OpenCL.dll, which is the ICD loader, and exposes all of the available platforms. It is provided by Khronos and redistributed by the OpenCL platform vendors. So go ahead and link to it; it will work with whatever is installed (although if nothing is installed your application won't run because it can't find OpenCL.dll; this is solved other ways).
2: Yes. As long as the ICD loader is the latest, you can get at the newer API on newer platforms / devices. Just don't use new API on old devices; that will crash or worse.