you didn't ask the aperture. not my fault at all.

Your question is which adjustment to start with: shutter speed or ISO?

My answer is: adjust shutter speed unless you could get a blurry image, then increase ISO.

BTW: I don't agree with adjustment of aperture in your answer. Aperture determines the depth of field. I will adjust as needed. Also modern lens have 'optimal' apertures (usually at f5.6-f8), which give the best image quality. A good photographer will try to stick with those. Wide open at f1.4-f2 will give you soft images.