There are so much blog in this world. Millions I guess.
Millions and billions
There are scripts that you can find online that can be added to your blog and it counts how many people are currently viewing your blog and how many people have been on your blog since a certain date. I have tumblr, and there are many blogs that have this.
a lot
Since blog is a pretty new word, there is none in Spanish (yet). You can use blog and people would understand, however.
It is for both comment and content sharing. Generally people use blog for promoting their business or interest.
No, but at Wordpress you can tell how many people read your blog and where they're from.
A blog title is the blog's name e.g. "No stupid answers". A blog address is the web address (URL) that people need to use in order to get to the blog via web browser e.g. http://nostupidanswers.com
Anyone can write the blog because blog is one type of information based on the particular topic, which will help people in many terms but if you write blog make sure that blog should be informative and helpful for people.
The most popular travel blog online would be Travel Today. This blog has many different people that write for it and is read by millions of people daily.
People who like to blog can be called blooks, if that is the nickname that someone wants to use for them. However, they would likely prefer to be called writers.
There are lots because most people in US have internet connection.
There are many free blog platforms - Blogger, Wordpress, Typepad, Tumblr. You can start an account in a few minutes at any of those sites. Blogs are used for writing, whether about personal life or a particular topic.
People blog for fun keeping in contact sharing photos and events.