Assuning you are in UK so hopefully this is relevant to you but not sure if you have spoken to solicitor but I have spoken to mine about divorce this week and this is what I was told.
Divorce comes in different parts in UK first you have the actual seperation and then you have the financial settlement and then there is agreeing what to do with the children.
So when it comes to the financial settlement you can do this at any stage and most people tie it into divorce proceedings to do in one hit. Solicitors will start at 50/50 and then they will go from there, they will look at everything from pensions to ISAs to stocks and shares and property. If it's an asset its included. If you've been together for long enough (think few years) it's all up for grabs regardless of how it came into your marriage. For example if you've had time off to have your children you will have missed out on pension savings whilst working so it's important to get things like his pension included. I also say start at 50/50 they also take into consideration who is the residential parent and this could even sway things so you end up with more. Do not back down just because things get nasty if you can stick it out you will still get your divorce and settlement and he will have to pay. You deserve to to give your children the best life you can.
Now down to children, there is not really 'custody'inthe UK, there is usually a residential parent and non residential parent which has some form of visitation. If you can agree a parenting plan between you then great, if not you will be expected to do mediation and then if you still cant agree it would go to court. Only once court ordered is it legally enforcable, therefore even if he says you give me all the money I'll let you keep the children he could change his mind after the financial settlement and fight you for them. Whilst you do not have a court ordered parental arrangement he has the exact same rights to you and could just not return them-would like backfire on him down the lime but in the meantime the damage is done as you haven't been able to see your children. If you think this is a tactic he would use you should do everything in your power to ensure that you only allow supervised visitation etc.
My solicitor also told me the courts would rarely go back on visitation unless there was proof that the parent was endangering or it was negatively impacting the child. For example if you got pushed into overnight visitation that you weren't comfortable with and then went to court to try and get a plan that would just be daytime visitation they would likely rule that its been fine to date so they wont go back to lesser visitation unless you can prove a good enough reason.
Also bare in mind that they will want the best for your children, they want to see that you are calm and reasonable and all your statements are coming from a place of wanting your children to have a good relationship with their dad and by having supervised visitation it would allow this as they wouldn't be negatively impacted by his behaviours when having to be solely responsible for them.
It's all a bit hard to go into specifics but I would recommend if you can talk to a solicitor it would help you feel more clear, it certainly helped me.