Verified answer

Can you?  Yes.  Will the Court Clerk accept the filing?  Yes, as long as it complies with the laws in your State.

Simply "not paying" for defective goods would naturally get you sued, unless you have properly notified them of the defects. You didn't say that. You may have numerous defenses and counterclaims that you might unintentionally waive (forever) if you or your company's attorney don't raise them in a timely answer.

While you are certainly entitled to draft and submit your own response, if you live in the US you should have tried to deal with the merchant first according to their grievance procedures. Since they're suing you haven't done that. Most companies are not liable for consequential damages either. 

All that said a lawyer would be your best bet. Maybe he/she could raise a defense you don't know that's available.

In my state, a corporation must be represented. An individual may appear pro se.

can you? yes. would it be smart to do so? no. hire an attorney

Yes, you can submit your own answer. Beware of representing yourself in court, however. An experienced attorney will destroy you there.

You can but it has to be done in the proper form in order to be acceptable to the court. Better to have a lawyer draw up the response.

You do not have to hire an attorney. If you don't you probably will wish you had.

You need to prove that they were defective and show that you tried to return and/or filed a complaint with the seller. Get a lawyer.    If you just kept the goods and said nothing, then you owe them for the products.  Write your own response if you want, but be prepared to pay up. 

You can but you will probably lose.