Don't Think - Do It . Just start a free or self hosted blog ( i would suggest managed wordpress Godaddy) and start blogging . Don't overthink about it .
Well you go and do it! What I would always say about an online business is that the financial risk is much lower than that of an offline business therefore there is a lot less to think about and worry about. Don't get me wrong it is hard work you can't just hit the mouse botton and earn six figures online as it doesn't work like that. But with hard work and dedicatilon you can make a success of it. What I have started doing on my blog (that I started monetising at the beginning of this year) was to put together monthly income reports so that I can keep an eye on its growth. You can have a read on the link below: http://myweightlossdream.co.uk/weightlossbloggers/category/weight-loss-income-reports/ And I wish you the best of luck and that it goes well for you.
What are you interests? Hobbies? Build a site around that. In building a site you will need a lot of content. If yiy are writing the content yourself and if you are not intested in the topic it will be hard for you to come up with content.