It's unlikely that he has done any research on the financial consequences of divorce before announcing this decision. So you can get ahead of the curve.
Re the split of assets: if you can't afford to buy him out of the house you will have to sell and move. I'm in this position and as upsetting as it is, it's just a fact. A house is just a house and I will make another nice (much smaller) home. However, although the starting point in divorce is a 50/50 split of assets, the actual split is determined on basis of needs. If you're going to have the kids most of the time and he only wants EOW, your housing need is probably greater (more bedrooms) than his (he can put them in a shared bedroom when they're there).
Your childcare costs are also relevant to needs because this drain on your income will reduce income available for rent/mortgage and other essentials like food, travel costs to work, and utilities. You need to put together an expenditure budget (Form E requires this) to work out your monthly expenditure on everything. A solicitor will give you a template but you can also work it out for yourself. You need to get housing particulars of the type of property you need in the area you need, eg 3 bedrooms in X town, and work out what the maximum mortgage you can raise is, as the starting point to argue for how much equity from the current house you'll need.
Then you look at mortgage deals and work out the monthly repayments on that. Put that in the expenditure budget and add a monthly amount for everything else: food, utilities, childcare, petrol, travel to work, clothes for you and the kids, road tax, insurance, car maintenance, house maintenance, holidays/entertainment, birthday and Christmas presents etc. It is also helpful to do a second budget of just the hard essentials (no holidays, presents etc.). If it looks like you won't be able to afford the mortgage you need on the basis of a 50/50 split of capital, then that's your argument for an unequal split in your favour. That said, he also needs to be adequately housed and if there genuinely isn't enough money to house you both then you may both need to look at moving further afield to cheaper housing.
Court will expect you to maximise your income by increasing hours.
Finally, if you have any shared savings accounts, I'd think hard about withdrawing 50% of those to an account in your sole name. My STBX had all our joint savings in a sole name account and had spent every penny within 3 months of leaving me. It was nearly £100k. I won't see my share of that back.