I have been thinking about your situation and this latest development on and off all day, and I don’t really want to overwhelm you with advice which might be unhelpful.
I think the first point I wanted to make was that I agree with self-care along the lines of what Gutterton suggests. I would probably add that I think it is okay not to be strong all the time - if you think about resilience, that is about bouncing back, not being on top of everything all the time. So be kind to yourself as well, this is a lot to deal with. Losing my job as a single parent ranks up there with something happening to my children as nightmare scenarios, so I imagine this is very scary.
I guess my focus would be - what real life support do you have, and what support can you draw on? Do you have a good relationship with your parents? Do you and the children have somewhere to go in an emergency? I am not saying you should go or would need to, I guess the question is if you were totally on your uppers, do you have somewhere to go?
If you can answer that question positively, then the situation becomes a bit less scary. Of course no-one wants to end up back at their parents as an adult, and I am not suggesting you will.
I suppose that would be my starting point to deal with the anxiety - to work out where my real life support is. (I already suggested contact Women’s Aid, I would still suggest that).
Then of course I do not want to end up at my parents, although they would have us - so what can I do to earn money? You have a business to develop. This is a big plus. Then on top of that, what benefits might you be entitled to as a family (try the Citizen’s Advice Bureau)
And work from there in terms of what you need.
Of course, I am talking about you, because this situation needs to be viable for you. What happens with your marriage is sort of an added extra which will sort itself out in time. RandomMess is correct that you need as much time to develop your business as he does to start up his.
So my advice would be to make sure that you have the time and resources you need, be clear about what support you have, and take it one step at a time from there. To that extent, what you need to do has not really changed, it has just become more pressing and probably more scary, but as previous posters have said, you don’t need to get drawn into his work plans, you do need to have a good handle on your joint finances and what needs done with mortgages and loans (hence financial transparency). One step at a time. Courage.
And if you think working on your business is pointless because all your mental energy will get sucked into his plans, then the simple answer to that is simply to say no. Be clear what hours you are both working and stick to it. Your business - your issue; his plans are his.