We had a similar requirement for one of our forms. What we did was to create a multi line text field called additional_guidance.
Then in the mouseEnter event of each field we had the following Formcalc:
additional_guidance = "This is further information about this checkbox"
On the mouseExit event we had:
additional_guidance = null
Alternatively, you could set up the root container as a flowed content. Then the checkboxes would be in a positioned content subform and subsequent fields in another positioned subform. In between these you would have a hidden invisible flowed subform which contains the notes in a text field or static text. This would appear or be hidden depending on mouseEnter events or click events on buttons.
checkbox1_notes.presence = "visible";
xfa.host.currentPage = xfa.host.numPages - 1;
checkbox1_notes. presence = "hidden";
xfa.host.setFocus(xfa.form.form1.p1.checkbox1); //this would be the full reference for your object