Be careful with two many emails/password etc.  Its easy to forget or lose a credential.  Some of the more secured email services also will delete old emails if you do a password revocery

No email can store your coin, you have to create an account from the coin wallet service, you can create a wallet account or some that support the type of coin you use

I use one email for most of my trading except my fiat account. I use 2fa for everything.

Just as it is safer to use a different password for each account, it is also safer to use a different email and user-name for each account. This applies to all online accounts, and not just cryptocurrency accounts.

Its better to create email for each account. Don't keep all eggs in one basket. And use really strong passwords with 16+ characters using low and up case and 0-9 with special symbols. Dont keep passwords in one doc or save it in encrypted archive or something else. And better to do it on usb without any information on your pc

Use different email for each acc

What exactly do you mean? Bitcoin nor Ethereum is stored in a mail account. They're stored on adresses. I'm not exactly sure what you're referring to here?

You want to use a different email for each exchange, or something along those lines? Would be better for your privacy, not so much for your security. ( But most exchanges have a KYC policy so i guess it doesn't really matter.)