Layout html letters to send to the mail?

Question

css

Good afternoon!
In general, I sat down to typeset a message that comes to the post office when registering, buying, and so on. There were several questions:
1. Custom fonts (google-fonts)?
2. Where to write styles in <style>or <a style="???">for each element
3. How does responsiveness work in email clients?
4. What specifically cuts off Yandex mail, Google mail, mail.ru and mail clients for mobile devices and windows? where to read it?
5. How to set background? Paint everything separately background-image, background-image?
6. How and where can I test emails?
I found a solution inlinestyler.torchboxapps.com/styler/convert but it does not take into account everything, especially for Outlook (207-2013)
7. What to do with outlook?

Answer 1

eduard.kozachek.net/blog/it/coding/%D0%BE%D1%81%D0...

Answer 2

Try to typeset in mailchimp, they have an equal visual and html editor.
You can also test there.