1) A little bit of everything blog is not a very good idea as- You will have the option of what to post, but the subscribers will fluctuate. I have experience with this.
2)You can advertise with PPC (AdWords is good) in the beginning.
3)Should be 500 words at the least, and generally the maximum is 2000 words. It is up to you. But remember quality over quantity.
4)The frequency depends on you. It is better to post once a month (an amazing post) than 10 crap posts in a month. Content is king remember.
I would recommend a 4 day gap.
Hope I have answered your questions properly.
Anything else? Feel free to ask