Sharepoint automation

Question

Hi,

 

1. I have maintain all data in excel sheet.  

2. created infopath library forms: Form A (External)& Form B (Internal)

3. Added content type now in library i can select Form A & Borm B content type on the ribbon bar file option in the library.

 4. I have added a Page and used Infopath web part (Form A-External used) & Used Query Parameter webpart as well.

 

Question: wanted to give this page only read & write permission so external/Visiors people can fill the information only?

 

5. Even on Same library a workflow is attached once the form submitted it would be display information in library

 

Question: if another user enter same ID and this ID aleady exist the information would be updated (old+New) how i achievd?