This will sound very very mercenary, however, do not let him have any paperwork RE banks/money till you have had a chance to look through everything.
Take a copy of his payslip and P60 and seriously I'd apply to the CSA immediately as you are now living apart. If you have his NI number, name and address of his workplace it will make the application so much easier.
Make sure you keep hold of your childrens passports and birth certificates as well.
To be honest I'd have binliners of his stuff ready for him outside the front door.
But then I'm a hardfaced bitch.
Also regarding freezing joint savings accounts, ensure you back up your spoken request with a written request, I thought I had frozen my accounts but apparently the bank forgot to do it.
Infact I'd change d/d's relating to your house to a bank account under your sole name and ensure you have enough money to be getting on with and then freeze all bank accounts.
Rally friends around, or at least tell one very close, practical friend.