Hi Carlos,
1. Save the Excel as XML format and add it as a secondary data source to your InfoPath form.
2. Add a validation rule to match a pattern with d\d\d\d\d\d\d\d as the pattern
3. Same as #1. Or, you could export it to a SharePoint list and connect to the list instead. Qdabra also have an XLS to XML tool which automatically creates multiple XMLs for rows and worksheets in your XLS.
Good luck!