How old are DC?
If they're teens I can understand it more, because they can basically choose where they spend their time. You can make it clear they're welcome round your place any time and you can explain to them your situation, so hopefully they'd understand why you did what you're planning to do.
Younger DC I think you'd just ruin your relationship with them completely, because they won't really be able to understand and I'm not sure trying to explain abuse to younger children is even appropriate, your marriage difficulties aren't their problem. It'd also ruin things for them by leaving them in an abusive situation they can't choose to walk away from. They'd see you EOW most likely.
If he was difficult about access to spite you, your DC might end up not seeing you ever again, at least until they're old enough to go wherever they like independently and by then it'll be too late, they'll have no relationship with you any more and years of his lies dripping poisonously in their ears.
I don't understand your stance on benefits. You take the savings (how much is there?), use it to house yourself and pay your living expenses whilst looking for work. Then once it's below £16k you claim UC. Forget about keeping it in the bank as savings (which could affect benefits), you're not in a position to do that, so use it for whatever you need.
Are there things like a marital home with equity in it, to be sold? Does he have a good pension? Any other investments? If yes to any of these, you can take ALL the money in the savings account and offset it against these other things in the financial settlement. You'd not be taking it out of greed but because you needed to house yourself and DC.
You can also put your expenses on the CC. Who cares if there's less available for him? Tough luck! He's financially abusive. If it's a joint CC you're entitled to spend on it and are liable for half the debt anyway, so may as well rack some up, because do you think he won't?
If it's his CC he unofficially allows you access to, ensure the things you buy on it after leaving are for DC - clothes, school uniform, winter coat, food (tins and packets last ages, like years, so stock up), bedding, toys. And do it quickly before he realises you've gone and cuts it off. Buy next size up for next year if you don't need it for this year. Keep all receipts as proof it was spent on DC.