For your first question, create a Callback function for that button. I assume you have somewhere an input field where the desired text is stored. Save that to a propery, lets call it desiredText. In the callback function, it should look something like this
app.desiredText = app.InputEditField.Value;
function ButtonPushed(app, event)
app.EditField = app.desiredText;
As that specific text is a property, you are also able to recall that text in your sendmail command.