What? I Have to Disclose My Finances?
Generally, yes, if you want to talk sensibly about what you need to live on. And your ex has to do the same. For your own sake, you need to be able to get a handle on your assets and debts, and you need to come up with an honest estimate about what your monthly income and expenses are likely to be, just to be able to sleep at night. The numbers you enter may affect child support calculations, spousal support payments, and certainly asset and debt distribution. So be honest with yourself.
It's helpful to use the Clark County Family Court's Financial Disclosure Form (FDF) as a starting point. You can find that form here, download it, and fill in as much as you can. What you can't fill in, you're going to have to research in order to estimate numbers.
This is a court form that judges look at in divorce proceedings but that does not have the same weight in mediation. Litigants who complete these forms have been know to demonstrate a highly refined skill of fantasy and ridiculousness along with a willful blindness to the fact that the judges reviewing them are smart people. I have personally witnessed a judge go through a litigant's FDF line by line and change the numbers to reflect reality. That litigant stood sheepishly while the false statements were exposed to all.
Remember that, unlike litigation, mediation is assisted negotiation and you and your ex will be engaged in trading things of greater and lesser value during the course of the process. The mediator will not be comparing FDFs and balancing them between you. The form's purpose is to help you convince each other that your needs are genuine, that what you are asking for is not specious. Of course, you'll need other documents to prove your FDF claims to your ex, but you should clearly have them if you're claiming them.
At the end of your mediation you should have a resolution that you both can agree with, live with and that does not break any laws. It may not be the same result you would have gotten in court because you are not bound to follow many of the rules of court. Of course, you must submit the proper forms, pay the fee, and file the paperwork. But you two can be creative in mediation in a way that would be denied you in court