From what you've said the 'work' he's done is no more than that which is usual to create or enhance a home for one's own pleasure rather than making substantial alterations/improvements with a view to increasing the resale value of a property.
Let's say that you realise a profit of £120k from a sale of your home, of which you can prove you put up £60k which leaves £60k minus estate agents fees to be split between you.
Deduct £10k from his £30k to repay the debt he owes your df and a further £5k for the car loan. His share is now £15k minus his 50% contribution towards sale fees ergo £15k is the ballpark figure from which negotiations downwards begin.
As for him being advised not to leave because it may 'damage his financial entitlement', that is pure and utter bullshit which he's dreamed up in order to be able to put the screws on you by tormenting you whenever it suits him.
Twunts like him are tediously predictable inevitably capable of deviousness because they're immoral little fuckers who don't scruple to use underhanded means in their attempts to get what they want, and what they lack in IQ they make up for in cunning.
But don't despair as there are numerous ways in which you can play him at his own game see him off.
I'm astounded, but not unduly surprised, that your police force appear to have been extremely lax in not putting you in touch with a dv worker or forwarding a report to SS as they are duty bound to do when dc are present at a dv incident.
Nevertheless, you have more than sufficient grounds to apply for occupation and non-mol Orders and I would suggest you locate your local Women's Aid branch here www.womensaid.org.uk and ask them to recommend a solicitor who specialises in dv/family law cases to get that particular ball rolling.
As living with this abusive arsehole has clearly taken its toll on you and, I suspect, reduced you to a shadow of your former self, it seems to me that you are long overdue for an injection of some serious lead into your pencil and I intend to turn my mind to that matter in my next response.
In the meantime, your first port of call should be a solicitor who specialises in dv as above because in order to level the playing field, so to speak, we need to flatten run a heavy lawn roller over him prior to commencing financial negotiations that will see you and your long suffering df out of hock to this odious man.