Can I ask about my SEO. I have a blog ranking in alexa 3million. The domain is blogspot.com. I am planning to buy a domain like .net or .info. My question is how it will affect my backlinks using blogspot.com are they will be remove in my linkings in alexa or not?
yes .. its will effect your ranking .. but you are able to set 301 redirection .. 301 redirection is helps you to get your traffic back . Check Google Webmaster tools to notice Google about your migration .
You can able to you 301 redirect now you can use blogger paid services so it will best, it's it's true it's cost is bit higher than .info or .net domain
I also recommend you that use 301 redirection for this purpose. And sure it will affect your ranking.