1. Whether or not interest is automatic on a settlement agreement that was incorporated into a divorce decree is currently in dispute in the courts (i.e., different courts disagree). Some courts believe that interest is mandatory, while others believe that it is discretionary. Therefore, all you can do ask. You can argue that its mandatory because the agreement is a contract
and the court's equitable powers were not used to determine the terms of the agreement. Even if the court determines that interest is discretionary, the judge may still award interest, and I see no reason he wouldn't, particularly when your ex has clearly breached his obligations.
2. Your illness will not affect the case (I'm terribly sorry to hear that! I truly wish you the best).
3. You can attach his motorcycle and sell it if it has any substantial equity. Obviously, that would not be possible if he has no equity due to a loan
. You can also attempt to garnish bank accounts, put liens on other property, etc. The fact that the trips and motorcycle were purchased, the fact that you have evidence that he works "under the table" and has more money than he admits, and the fact that he refuses to pay you what is owed will likely work in your favor with regard to interest, and it also may convince the judge to hold him in contempt and possibly even jail him until he comes up with some money.
I hope that helps. I truly wish you luck! Please remember to click "accept."