You can use the SplitText processor to create multiple flow files for a large block of text.
To replay the file periodically, you can use the GetFile processor to read the file - there's an option to 'Keep Source File' so that NiFi does not delete the file once it pulls it in. The processor additionally will have a schedule when you click into the Properties - you can set this schedule to 5 seconds, 5 minutes, or anything else you'd like.