What is the best kind of professional to help me deal with issues about protecting my finances post divorce?

A lawyer would probably be your best bet because they call tell you what you ex is and isn’t legally able to go after post divorce. Depending on your situation, there may be things that he is entitled to, so talk to a lawyer. Good luck.

I would discuss this matter with a good divorce atty first, then ask for a referral to a good financial planner.

The attorney will help you keep what’s yours and the financial planner will help you keep control of your money and assests once they go into just your name.

If you are the US, remember, anyone can be sued for any reason. No matter how you protect yourself your ex can sue you.
You don’t need to answer these questions here. Answer them to yourself.
Why is he after you? Is he trying to recoup something he believes is his?
Is it so important to him that he will spend 3x the amount it costs just to get it? Is it possible to have a civil discussion with him or are you both well beyond that point? Can you look in the mirror and say you did the right thing (treated others as you would like to be treated)?.
Personally, I would give the appearance of living very conservatively while hiding my savings and assets until the heat dies down.

Start with the attorney. If you have assets now, then you can’t change that, and depending on your state your spouse will probably be entitled to a portion. Some considerations will be how long you were married and if there are any children involved.
As for future income, talk to your attorney about the implications. I wouldn’t be starting any new endeavors until after the divorce is final.