Difference between these two parameters sonar.branch.name, sonar.branch.target

Other queires:
1.)Email notification capability for sending the scan results to our internal platforms.
2.)Rule customization for existing rules and removal of un wanted rules as per dev teams suggestion.

SonarCloud supports webhooks, along with some basic notifications (check your user account. Webhooks are probably the best way to notify an internal system a scan has completed.

You have the power to change the ruleset by adjusting the Quality Profile for each language.