Hi Liorlankri,
As specified in case2, u should create a Dataconnection to the web service.And u should create a "Receive" data connection to ur web service.
By using "Receive" dataconnection,u will be able to send data from ur form to the webservice and also receive data from ur webservice.
And regarding ur 3rd question, u cannot do it without using a webservice becoz u donot have an option to query the database when u establish a "Receive" data connection to it.
Now to avoid installing .NET framework in users machine, write JScript code to query the "Receive" dataconnection to ur webservice.
When querying, donot forget to pass the "IDNumber" to ur queryfield in ur secondary datasource.
regards,
Abhishek