During the separation think about what you will need-- financially speaking. Is he going to be paying half of housing costs for you and your son? Do you work or are you a SAHM?
Is he going to keep paying for the cars too?
Write up your monthly budget-- everything from rent to utilities, down to new socks and toilet paper. (Dog food!). Submit your budget asking for the percentage your need-- in my case he was expected to keep paying a portion of all house bills, groceries, utilities, etc because I was working part time.
Separation is supposed to be short term, but think long term.