@Lisawr
I agree w/PPs that you should acknowledge his email with the thought that if you don't he may be prompted to 'go official'. I think I'd say "Noted. I will respond in due course". That doesn't give any specific time frame.
And get yourself to a solicitor as soon as humanly possible. I know this is a bad time for appointments, but I would try and keep trying until I found one who has openings next week or the week after.
You need to be in full 'protect my assets' mode. He certainly is and he's shown that he has no scruples. You cannot trust him to 'play fair'. He's guilty as hell and like most guilty people, they'll make themselves feel innocent by becoming angry and turning themselves in to 'the victim'. The focus of his anger will be you and is usually followed by the need to 'punish' the person they know they've wronged. Why? Because you are living proof of their 'sins' and a reproach to their actions.
In the meantime, you need to be copying any- and everything you can get your hands on regarding finances. Copy/print online financial statements & records and scour the house for paper documents. He's gone for now, so now's the time to do it. Locate all vital records (birth, marriage, passports). Then get all these documents OUT of the house if you can. Ask a trusted friend or relative to keep them for you. If you can't get them out of the house, hide them as best you can. If you have joint banking, consider moving half into your sole name. If you have any income of your own going to a joint account, open a sole account and have it go there.
And I'll pass this on from personal experience. I'm currently undergoing a legal separation. My attorney told me that if I was going to 'make any financial moves' to do it before any legal papers are filed as once things 'get official' you usually aren't allowed to make any changes. I was able to take half of our joint account and open my own before I filed legal papers. And it's a good thing because he cleaned that account out, not knowing I'd already moved half. I was also able to remove him and name my children as beneficiaries on non-community assets as well as close a joint credit card. There are other assets I couldn't do anything about, but I protected what I could.
I know you're devastated, I know you're hurting. But right now you can't afford that. Right now you need to channel every emotion into action. Protect yourself. Protect your children. There will be time later to grieve, I promise you.