starting a blog - advice

I've wanted to write a blog for a long time, so I may as well just get on with it right?! Writing and reading are my favourite hobbies!

Has anyone got any tips for starting out?

A recommendation for which site to use would be fab!

Is it best to pay monthly at the start for a better one?

How do you get paid for it through ads etc? (sahm - just in case I manage to do well or interest enough people haha)

I want to write about environmental issues and how to create positive change in your lifestyle. All stuff natural really. Do you think this is an interesting topic? No already done too much?