Dear Sajan,
Relay Server is recommened for MBO Based apps. I believe your Hybrid App is based on oData services.
Reply to point 2. However, you can still user RS with SMP 3.0+. I am not sure if you are using the correct command/add the complete details in rs.config file. Please refer to this link which has the full example of the file.
http://help.sap.com/saphelp_smp303svr/helpdata/en/ca/2cac530b72497c832227711221ef0d/content.htm
Once you make the changes, please try to update it with the command ---- Ensure you have the bidirectional ports opened on the RS and SMP.
Reply to point 3 - I don't think you need to make any changes in the services. During the app registrations you will be using the RS server instead of SMP server details once its setup and the communication should be established successfully.
I would like to loop Jitendra Kansal to confirm on point 3.
Regards,
Nagesh