OK, answered part of my question from reading ColdFusion11_Installing.pdf . (of course )
"You can upgrade from ColdFusion 9 or ColdFusion 10. When upgrading, the installer preserves the existing settings and installs in a new directory, automatically assigning ports that do not conflict with the existing installation."
I now need people's experience please.
Create a car (archive file) in CF 9 enterprise which will capture all CF 9 settings like Data sources, Web services etc. Make sure when you are doing this, pop up blocker is disabled.
NOTE : While creating the archive file, give the full name with the absolute path in the package name. For example C:\Test\mypackage.car
Then move this car file into the server where you want to install CF 11. Install CF 11 and then deploy this archive (car) file. All CF 9 settings will be migrated to CF 11 enterprise.
Else, if you want to install CF 11 on the same server where CF 11 is installed, then remove the connector for all the websites which are configured with CF 9, make sure the CF 9 services are running and then run the CF 11 installer and at the end of CF 11 installation, you will get a dialogue box which will ask you to migrate CF 9 settings in CF 11.
Run the Code Analyzer in CF 11 Administrator to check whether any the CF 9 code used in your application is breaking in CF 11 or not