Thank you for your question.

The plaintiff can move to have you defaulted at any point after you have failed to respond. If you respond before the default is issued, you are safe. Therefore you should respond as soon as possible. If you get defaulted, you can file a motion to open and file your response. These are usually granted where the failure to respond to the lawsuit timely was not intentional.

Yes. And if they do file a default motion after you have responded, you can file an objection the motion indicating the date you filed your response.

Yes, you can deny the allegations in your answer.

If the litigation is malicious and baseless, you can sue the plaintiff after the conclusion of the lawsuit (as long as it is dismissed in your favor) for malicious prosecution. If the statement was made knowing of its falsity, you can ask for sanctions to be imposed.