Blog for the fun of it and show character. It is immaterial how many write about a particular subject, it is how you write the matters.
Post Ideas: At times you will just run out of ideas for post not sure what to do. use google and apps like Evernote to note down all that ticks in your mind. Something will surely turn into a new post.
Respond with personalised comments rather than a generic Thank You. Fostering a conversation helps build the credibility of your blog!