OP my DH ex tried to screw him for absolutely everything, she too checked out of their marriage, established a new partner and then tossed my DH to the kerb.
She even got DH to take out loans in his name when she was already having an affair.
DH was too nice to start with, but after a bloody good chat with a decent solicitor he stood up for himself and never backed down.
We got together half way through a 3 year legal battle. Some things that may be relevant to your situation.
If your ex works and pays her own bills etc then she won't get spousal support. You were only married for 7 years and you could even say separated for 2 of them? My DH was married for 10 years and it wasn't classed as a long marriage so the assets got split 50/50.
What did happen in my DH case is that he got a charge on the former matrimonial home. But as it looks like your ex doesn't live there and covers her own rent (may have misread) I cant see why you can't split your assets and only provide child maintenance. Both parties are entitled to want money from the settlement to rehouse, and please this has to be somewhere suitable for your child to stay. Aim higher than some grotty bedsit, and work your way down from there.
Also my DH agreed as part of settlement that the ex pay him a set amount each month to cover the debts she made him take out. So I would say it doesn't matter whose name your debts are in but push from the beginning that she takes ownership.
DH also named his ex's affair partner right from the beginning as to why marriage brokedown, and although your ex may never move in with him, but if they do co-habit that will certainly make a difference.
DH ex denied their relationship at first but as the settlement dragged on as DH stayed firm and years started to tick by the ex had to finally admit to co-habitting, which they had started to do not long after divorce proceedings commenced. His finances were then taken into account when it came to the ex's housing needs. Of course I had to disclose mine as well, but the point is you want a fair settlement that is right for everyone.
I would from now on keep all communication business like, and preferably in writing. Don't discuss the divorce with your ex unless via solicitor or at least upon their advice. Keep direct communication about your son and make sure the only person prone to rants and silly demands is your ex. You need to be seen as being reasonable, the judge will soon work out if you do that it is the ex whose out to get everything they can whilst you are only being fair.
Good luck, and I hope you get yourself a good solicitor to fight your corner. X