Finances upon separation

I gave up a lucrative career when I had my two kids, I have been financially and mentally controlled. I am trying to gain confidence to leave my husband and have a pt job for 16hrs per week.

My question is how much does he have to keep paying until a divorce is underway and until we go to court to arrange finances re house and spousal?

I believe it is a simple sum of bills and living expenses less what I bring into house equals what he has to pay, but how much buffer do I give myself, for example if bills etc come to £2k and I bring in £1k he would have to make up the other £1k but I would not have any disposable income?

It's based on needs and ability to pay so depends to a large degree on how much he has.

You can't just do it as a simple sum like in your example because what if he doesn't have a spare £1k per month after his own expenses?

Are you claiming all the benefits that you are entitled to?