How do I create a template for my apple keyboard to fit along the top row of keys to aid note input?

I don't have a template, but related to your idea...
It may be helpful if the note entry toolbar itself could (as an option) display such info.:

But it should be easy to create with MuseScore. Some suggestions, I didn't check it: Insert the desired notes, use staff text for the numbers, if necessary, change the horizontal offset for the chord inside the inspector, right click->instrument/staff properties... and select invisible barlines and deselect show time signature, key signature and clef; also if necessary use the image capture to save it as png or svg, or decrease/increase the scaling in page settings before.