If you do nothing else OP, get involved with women's aid and attend their meetings. It'll give you advice and a supportive network of people who understand what living with this type of man is like. It'll give you knowledge about relationships and knowledge about how to leave. Give them a call tomorrow to find out when the meetings are or find the address of your local branch and just show up. Someone will talk to you even if there's not a meeting on.
Essentially, you need to get your ducks in a row, as they say on here.
Forget about money that's already been spent, it's gone. If it makes the house more valuable for when it's sold and the proceeds split or just makes it more sellable, those are good things.
For tonight you need somewhere safe to sleep. The DC room?
Tomorrow start gathering information. You need all the financial information and your marriage certificate etc. Try to get copies of everything that's official or financial.
Book an appointment with a divorce lawyer when you're ready. You don't need to start getting divorced just yet but empower yourself by talking through your options and what happens. You'll also already have a lawyer if he suddenly springs divorce on you. He's threatened it and it may be an empty threat but it also may mean he's in the process of hiding money and preparing to start divorce proceedings. So get yourself prepared even if you decide not to act just yet.
If you're concerned about needing a backup plan and being homeless, register with the council. You're currently housed so you'll be way way down on the priority list but it may make you feel safer to be in the system and if the abuse escalates you can update the information.
Go onto Entitled To website and input your information hypothetically as if you were a single parent, that'll give you an idea of whether you could claim universal credit or other benefits and how much it'd likely be.
If you're not already working, think about what needs to happen for you to get back to work and start taking steps to do that.
Start building savings from whatever you can. Selling things online which you don't use any more, being frugal with everyday spending and putting anything saved aside into an account in your name. Ensure the child benefit is going into your bank account not his. If you're not already claiming it then claim it, don't worry if he earns too much, he'll have to pay it back and you'll get to keep it. That's the system and it's legally allowed.
Ignore his threats about taking DC. You'd have to be a truly terrible mother for the courts to award him residents parent status and you no access. Almost certainly you'll be the resident parent and he'll probably disappear from their lives. Once you've split up you can claim child maintenance, but consider whether you want to. Personally I think half the men who have their DC at all only do it to pay less/no maintenance. They seem to fob off the DC onto the nearest woman they can find whether that's their own mothers or a new girlfriend. Others basically neglect or semi neglect their DC if they've nobody to fob them off onto. If you don't claim maintenance I think many men would just disappear altogether. Which might be a while lot easier than co parenting with an abusive arse.