Legal seperation

I just moved out from living with my husband. We have a child together. I know custody is something we will need to adress, but my immediate concern is the legal seperation. What do I have to do to protect myself. All the property we own currently are our cars (1 each) I am going to have to buy another one (mine has had it) and would also like to buy a home within the next 6 months. Do I need to file formal papers to protect myself so he can’t go for half, or if we make an informal agreement that we’ve seperated our properties and any debts or properties we gain after this date are each our own and sign it, is that sufficient? As far as custody goes, I know it can get expensive, and my daughter hates going over there. Are there any suggestions for that? Is there an affordable way to handle the custody/visitation. I don’t mean to sound cheap but seperating has drained me financially. I’m just lost any advice about seperation, and custody would be much appreciated.