I have been in exactly your position. He was paying nothing, self-employed, total liar. I couldn't afford a solicitor. He turned up in court with a solicitor AND a barrister.
This is my advice to you:
You will be ok representing yourself if you can hold it together and stay calm.
BUT you must write down the factual points you want to put across and stick to them. (I was totally intimidated and bullied by the lawyers. I felt upset and confused and I made a real mess of it because I hadn't written down my points and kept getting sidetracked.)
He will lie about his earnings. So you will need to demonstrate that his lifestyle proves that he is lying. For example, if he only earns X amount, then how is he able to afford a legal team, a fancy car, his house, holidays, etc. (You get the general idea.) List everything. Are you able to find photographs on social media you can use as examples?
Does he have a history of lying? If so, give examples that you can prove.
Did he have a history of financial abuse during the marriage? Again, give examples if you can.
You do not have to co-operate with his solicitors. They are working for HIM, not for you. Do not engage with them. (I made this mistake.) You can send any evidence to the Tribunal Court at the court's instructions.