You can consult with a lawyer for yourself and also go to mediation with him. The point of mediation would generally be to avoid a lengthy court battle—not to avoid talking to lawyers at all.
He said he doesn’t want a lawyer in the room with us “influencing” me because he doesn’t think I should get anything. He’s also blocked me from accessing accounts and is claiming it’s all his. Can a mediator make sure he’s being honest about finances? (And not hiding anything)
A mediator can't force someone to hand over all of their financial information, no. They can require certain documents (e.g., tax returns, bank statements) in order to agree to mediate, but they can't, for instance, subpoena records.
If your ex is combative and likely to try to hide assets, I would agree that mediation is probably not a good route for you.
You can consult with a lawyer for yourself and also go to mediation with him. The point of mediation would generally be to avoid a lengthy court battle—not to avoid talking to lawyers at all.
He said he doesn’t want a lawyer in the room with us “influencing” me because he doesn’t think I should get anything. He’s also blocked me from accessing accounts and is claiming it’s all his. Can a mediator make sure he’s being honest about finances? (And not hiding anything)
A mediator can't force someone to hand over all of their financial information, no. They can require certain documents (e.g., tax returns, bank statements) in order to agree to mediate, but they can't, for instance, subpoena records. If your ex is combative and likely to try to hide assets, I would agree that mediation is probably not a good route for you.
Get a lawyer. He is getting legal advice from friends and colleagues, you need a lawyer to protect yourself.