Email still is 2-factor though it is easier to compromise, but I would recommend using the sms 2-factor if you can. Much safer.
You cannot think of email as 2FA. All it takes is a keylogger or virus to get your password and bye bye Bitcoins. Never rely on email for so-called 2FA!
You can. It still provides an extra layer. Plus, my 2-factor email goes to an address I only check on my phone so it's safe and completly unlinked to my computer.
If your email has 2FA as well like I recommend then it is much more secure. However email without 2FA it doesn't provide an extra layer at all as if someone has your email they can reset your wallet password. However you should also have another form of 2FA (like Yubikey) on your online wallet as well. Then you have double 2FA and less chance of you becoming the next horror story.