If I file a motion to compel discovery in which my ex did not disclose severance pay of 185,000, how much sanction can I request? Would $5000 be reasonable? Can I get the amount that would be due to me based on child support guidelines in a lump sum or does it need to be prorated?

Litigants do not request and amount for sanctions. A sanction, if imposed, is decided by the judge. You may suggest that the remedy for his prolonged refusal to cooperate be an amount of back child support you would have received based on the income left undisclosed.