Ask your ISP how much their service cost per email they should be able to tell you.
Yes, Gmail is an email system.
Depends on your email I think. I know maybe able to send it like an email. And if you have Gmail maybe able to do it with that too. You never know if you try. It shouldn't cost you anything to send it.
You can send mail from gmail to other email id the same way as you do it for gmail IDs.
Yes, it is possible to send it. It is because Gmail is able to send data to different services too. Gmail can send an email to Live too.
Yes
You need a recipient ID to send an email. If you do not have any ID, you can't send the mail. To send a mail to naver, you need his Email ID.
You can send images to Gmail via phone also. You need to have Gmail signed in on phone. Then compose a Email and click on attach.
You can send mails from Gmail to other mails. Gmail allows sending to yahoo, hotmail etc. This increases the functionality and it's scope.
You can send effect designs via attachment in email. The size in Gmail is limited to 25 MB only. After that, it should be sent via Drive.
You have to compose the email to send. The sender's name has to be put in. The subject of the mail is optional if you want.
You can send chat request to your friends on GMail if you know their email address.