Create a Back end and fron end application using codeigniter 3

You could try starting with http://cibonfire.com/

Or perhaps if you want even more, any of the great CMS's built with Codeigniter. Just google for them.

There are also quite a few member authorization libraries available too.

If I was doing a blog I would use Wordpress or Ghost or similar. Depends on what you needed. If it is coding practice or for your own pleasure, then continue from scratch. But perhaps start with something a bit simpler than a blog, which can be quite complex if you are to achieve any level of sophistication with it.

People often think they need a blog when they don't. If it is your site and you just want to publish content then a blog may not be the best way to do that. It is very simple to add content, perhaps you might want to consider that a diary type date based presentation of your material may not be the best approach. Then again, it might be, it all depends on what you are aiming at.

Hope that helps,

Paul.