Definitely don't move out of the house or leave your children with him unless you want him to become their main carer. Going to court later to get them back will be complicated as courts don't like to see big changes to current arrangements and try and get you to agree on arrangements while they drag things out work through their process.
If things get nasty or aggressive you can get him removed from the house. But the same can also be said of you. So you just have to deal with it and keep things 'calm' for the sake of the children. Do document every incident that occurs, don't ignore any aggressive or violent behaviour (see a sol if it gets that way), and don't be dragged into any arguements as he may well be doing so to get you out of the house.
You can be separated but living in the same house until the divorce/house is sorted. Look on gingerbread and Families need fathers websites to get more info, advice and help with your situation.
www.fnf.org.uk/about-us/aims-and-objectives
www.gingerbread.org.uk/portal/page/portal/Website
As your youngest is under 7 you don't need to worry just yet about working. However this new government is planning on lowering the age (of your youngest child to 5) at which point you will swap to JSA rather than IS. You will then have to actively search for work and not automatically be entitled to benefits. Something to bear in mind for teh future but not to worry about just yet.
CAB can help if you have legal questions or need advice with benefits etc. A solicitor can give you 30 mins free time before you have to pay. If you have specific questions you can of course ring round and use a different solicitor to get another free half an hour if necessary. Don't spend time on preamble and waffle nicetiest. Get straight to the point and try and do as much research before hand so you know what you need to ask before you go.
Definitely get legal advice re divorce and splitting your assets. No matter how much you trust your ex to do the right thing when it comes to divorce even the nicest partner can screw you over.
If you can work out the arrangements wrt the dc without a solicitor so much the better and it will save you all years months of angst, court appearances and money. However you may be able to get legal aid if you have no money coming in apart from benefits and have no significant savings. A sol will help you apply for this.
Look at this website for details on shared parenting arrangements. Please bear in mind shared parenting does NOT mean equal time. It means equal responsibility for your dc and for them to know they have two equally important and significant parents who are still a very important part of their lives
home.clara.net/spig/
Good luck, and stay strong. Things will get better for you in the long term, but it will take a long time before that happens. Don't try and rush through the grieving process. You are losing your relationship, your future and your life plans and it takes time to deal with it all like any loss does.
Come here for help, advice and support. There's plenty of us around who you can turn too.
Best wishes