You do not have to write perfect English to run a blog, so do not worry and you will improve it with the time aka pratice. Another thing is that even if it is a blog, the main focus is on pictures and videos that you add along with it.
It depends on the topic, but you do not need that many words at all. You can start with 50 upto 100 words per post and then see if they rank, but make sure to write an unique content so do not rush it.