You can use Forms to create a poll and embed both the form and the results it produces to have a live poll.  But, to be honest, it's not a user friendly way of adding a poll.

Simply create a form, click SEND and copy the embed code which can be pasted into an embed section on Sites.

To display a chart of the responses, click the Responses tab and then the spreadsheet button to create a new Google Sheets.  In your Drive, open the responses Sheet and create a chart from the Insert menu.  Then publish the chart using the File menu.  In the options you can choose to get embed code, choose to select just the chart and choose to get it as in interactive element rather than a static image.  Again, paste the embed code into an embed section on Sites.  The chart on your site will be updated every two minutes.

A comments section can be added in the same way: but adding a form and embedding data from the results Sheet.