If you already have a counsel, trust their judgment. In terms of strategy, whether or not you fight depends on various factors (IP lawyers will go into much more detail). Your current cash on hand, the value of the IP and how central it is to your business, and frankly your willingness to fight will determine whether you just settle or defend the claim.
You can also contact the press, if your lawyer agrees, to put pressure on the troll.
Assume that whatever you tell them is going to potentially hurt you if they decide to take it to litigation. Contact a lawyer to at least understand your options.
Unless and until someone actually files a suit, a startup should probably ignore any trolling activities. If you are raising money, a regular part of diligence is to disclose any pending legal actions. There are differing interpretations about whether a demand letter constitutes anything like legal action. But, failing to disclose might constitute a breach of your duty to disclose, and disclosing it might make them want to go away.