Hi @Boopathi,
Regarding the selectors, I would in general rather be looking on a way to make them for steady, using wisely wildcard on the part they differ rather than having them recaptured every time.
When it comes to configuration of a project, you would recommend you to take advantage on ReFramework and its config file (Data\Config.xlsx, the Orchestrator assets.
Finally, if you are using the Orchestrator,having arguments for the jobs themselves can be helpful if you need variant in every run.
The feature is available from 2018.3
https://orchestrator.uipath.com/v2018.3/docs/about-input-and-output-parameters
Regarding Crendentials, you can have a look on the post bellow. It is not a best practice to store them as plain text, you should use either the credential manager or store them in the Orchestrator.
Once again, ReFramework is quite handy for credentials, with its GetAppCredential.xaml worklow.
Cheers