1.) An extension was files. Do I need any information regarding the extension to be filed with the 1120s? - No you do not need to include the extension when filing the 1120S.
2.) Do I need to file any additional forms/documents with the 1120s? - Generally not, unless you are making elections or something of that nature.
You don't need to attach 1099S or something of that nature.
Am I supposed to include a copy of any financial statements as supporting documents? - No this is not required. It is a good idea though to keep your supporting documents for 7 years.