Affiliate Marketing Secrets

I’d like to start a blog, not to make money, but to organise my writing and to make it accessible to a larger audience. I am aware that I need to narrow down my blog topic so as to be able to market it effectively. I would like to write about current affairs and prominent issues in politics, law and technology. Is this too broad a niche?
I’m thinking the following sorts of posts:
– Opinion pieces
– xyz subject explained: e.g. something in the news put into context and explained simply
– Personal life columns: light-hearted, off-topic posts about things I encounter in my life
– Tech how-tos/guides