Yep, forgot to mention: When you're set up this way there's little point in AF-S. When you're set for AF-C and AF-ON only, a single press of AF-ON is AF-S. If you need to track something you just hold down AF-ON. That's AF-C.
Remember, back in the film days -- at least before the end of the film days -- focus wasn't coupled to the shutter release. You focussed and then you released the shutter. It was two separate operations. Still should be.