To achieve your desired result, you need to use the HTML <sup> tag. You need to write the element you want to display at the top like this: (PO4)<sup>3</sup>
Also, you need to enable the Use HTML for answers option.
As to the second question. At the moment, the plugin is designed like that and an input must be there. Unfortunately, it is not possible to insert an Editor there.
FYI, please note, that the HTML <sub> tag lowers your desired text down.
Please check this and let us know if you have any further questions.