How Do I build Authority Sites?

2. what blogging platform is best for building Authority sites?
I love wordpress
3. How to generate traffic to such Authority sites?
If you not in hurry try SEO. Not free initially
4. How To get Backlinks should one do for such sites and what type of backlinks?
Try to get backlinks from quality sites with high PR. Oftentimes you will need some money to get it.

You must be extremely passionate about the topic you're writing for, because it'll need to be exceptional quality. Needs to be good enough to surpass every other post that's in that search term, in terms of quality. Those fiverr article writing services will not work. If your quality is amazing, the backlinks will follow for sure, after you do a bit of advertising. I never do Black Hat SEO on my exceptional articles, it seems that the backlinks flow in, after a little bit of online advertising. Moreover, you're going to have to guest blog a lot, to get those high PR backlinks. Comments just will not cut it.