Defamation that is actionable in court in the United States consists of a false statement about a presently existing fact that damages your reputation and is not a matter of opinion. While not strictly required in a case involving private parties that is not a matter of public concern, most defamation cases require proof that the false statement was made knowing it was false or with reckless disregard for the truth (which basically means with no factual basis and no ability to know if it is true or false). Hyperbole is excluded. Statements made to you personally cannot be defamatory, since you know the truth.
For example, claims that you were falsely called mentally ill might be considered statement of opinion or hyperbole. Similarly, if the person who said you weren't being hacked actually believed this was true (e.g. the pastor's assistant might believe this based upon what the pastor who was knowledgeable about computers might have told the assistant), then that might also not be actionable.
Most states have quite short statutes of limitations for defamation. For example, in Colorado, the statute of limitations is one year from the date that you learn that a statement was made to another person. Some kinds of defamatory statements (slander per se) do not require proof that you suffered actual damage to your reputation. Other kinds of defamatory statements do require hard proof of your economic damages.
Harassment does not neatly fit into one legal category. There could be claims for intentional infliction of extreme emotional distress, for breach of fiduciary duty owed by a pastor to a parishioner, for sexual harassment if factually appropriate, or for retaliation for certain kinds of lawful conduct. None of these are particularly easy to prove and again, the statute of limitations is not terribly long, typically two or three years from an incident.
Both defamation and harassment claims would be subject to first amendment immunities to the extent that they involved a religious official who could be legitimately characterized as carrying out a religious function in making the statements. Given the events you describe, this is probably a weak defense, but it would certainly pose one more hurdle to a lawsuit.
Another remedy for harassment and stalking, in addition to or instead of money damages in a lawsuit, might be to seek a restraining order against the people who are the source of the problem if you could really prove it with evidence that is admissible in a court of law that a judge would be likely to find to be more credible than the lies that they try to tell to defend themselves in court.
Finally, many forms of hacking violate state and federal laws and one of the federal laws, at least, contains a right to bring a private lawsuit against the hacker to enforce it. The first amendment religion and free speech clauses would not generally protect any hacking activity either. But, proving that someone is guilty of hacking, even in the face of strong circumstantial evidence, is often very difficult. For example, even if you can prove that the hacking originated at an IP address belonging to the pastor, proving that the pastor was actually the person at the keyboard and not a friend of his or another family member of his, might be quite difficult to prove. Also, as in the cases of defamation and harassment, quantifying your money damages could be difficult.
Stalking and hacking are also both usually criminal offenses so you could file a complaint with a law enforcement agency, although many law enforcement agencies lack the ability and competence to understand and investigate hacking cases and the inclination to deal firmly with allegations of stalking.
There are practical steps that can be taken to prevent hacking from a technological angle, although I am not competent to tell you what they are, and your post doesn't provide sufficient detail to know in any case. Obviously, this isn't a legal solution.
You can also be mindful in your daily life to act in a manner that mitigates your exposure to stalking although there are limits to how effective this non-legal solution can be as well.
You can combat character assassination with non-legal PR and counter-gossip approaches as well as with lawsuits.
Ultimately, you need to decide what to do and may need to confer with a lawyer and give that lawyer detailed factual information to evaluate your claims, and you may or may not decide that the legal system is a good solution. Proving incidents in a he said, she said situation, especially when one of the people involved is an outwardly respected pastor who has no qualms about lying and gas lighting, can be very difficult - so in the absence of proof, you may need to figure out how to develop proof before it is sensible to sue and you may not have much time to do that.
You are unfortunately in a situation with no easy solution, just a variety of second best options, and you have to decide which ones to pursue. You also need to focus not on what remedies the law allows, or what wrongs have been done by the perpetrators. Instead, you need to focus on what will maximize your personal well being.
Some people find that litigation can bring closure and relief, but ultimately, you can't control what the criminal justice system does and you have only partial control over what happens in a civil lawsuit. The litigation process prevents you from letting go of the matter if you later decide that is what will serve you best, can be costly, can be unjust, and can be aggravating. In terms of time, treasure and its impact on you emotionally, it can be a very expensive solution and can force you into a position where you are not in control. If the court finds that your evidence isn't solid enough, you could end up worse off, rather than better off, as a result of a civil lawsuit. And, usually, you can not get your attorneys' fees as part of your damages in a civil lawsuit for defamation or some kinds of harassment (such as intentional infliction of emotional distress) even if you prevail.
Ultimately, a court in a civil action for wrongful conduct can award you money, but can't vindicate you morally or remove that person from his position in the organization. Also, if you win a money judgment, you still have to identify assets or income from which you can collect it and many of these claims would not be covered by any insurance policy.
And, ultimately, a restraining order, while potentially a helpful tool in helping to get the wrong doers to back off, is just a piece of paper stating your rights and describing conduct that would be wrongful and punished if proven, not a magical shield that prevents someone from violating that restraining order just as they have violated your dignity and reasonable expectations of civil treatment and probably your legal rights already.
You have to decide what your personal objectives are and how best to achieve them without getting unduly focused on the limited and imperfect options that the legal system provides.