You say you've got e-mails documenting your work. These should be sufficient along with your payment records, tax returns and so on to show fundamental terms of contract:
offer
acceptance
sealed with consideration $
Simply sue for what's owing on the basis of your e-mail records. As long as they show agmt to perform work for consideration, you can send a demand letter followed by a writ/statement of claim (outstanding debt) and if the yoicks thinks you're not serious, you might very well obtain a judgment against him, which will give you AN ABUNDANCE of remedies to realize the debt plus interest!
So stay away from Tony Soprano and use your own maverick skills to get your money.
To find out how to serve a writ and prepare a statement of claim, visit local law library (open to the public always) and ask librarian for statement of claim precendents for simple contract debt.
You could also hire atty to do all this for you and claim the fee as a business expense!
The only way debtor might countersue is if there is no debt and you have somehow communicated that s/he is a deadbeat and not to be trusted (defamation).
Go maverick! You can do this without Tony Soprano collection agencies!