Apologies for late reply, I had forgotten to reply yesterday after work.
Yes, since the degree was awarded by the Singapore university and only the Singapore university, I believe just a single entry with Singapore as the Country of study will do.
And yes, for the eAPR (post-ITA) include your certificate and transcript alongside your educational credential assessment report in the upload slot for education documents. You can add your language test reports to this file as well.
And yup, be sure to include the stint abroad in your address history and your personal history, and make sure that the start and end dates are in sync. If you feel the need to add a short explanation to clarify the situation further, you can do so in the Client Information document. The upload slot for that is located at the bottom of the documents upload page, but it does not always appear so you may need to re-login until you see it. Once it appears for you, you can make it stick around by uploading a blank placeholder document.