Requirement Traceability Matrix

The would be before. Requirements should already be tracable from Review activities since you should have tracability in the Test Plan already.

This question also would depend on the organisation. If the organisation do test after development started then requirements must be already tracable to their source.

To make life simpler, use a tool to manage requirements.

After test cases are written.
We have to map test case ids with requirements for that we need test cases to be prepared.

Correct me , if I am wrong.

It is prepaed  to cross varify test cases and test script with user requirment .

It is very important from the testing prospective. Where we map the requirements with test cases. By preparing the RTM we can ensure that we have covered all required functionalities of the appln in our testing