Supply Restriction on Bitcoin & Bitcoin Cash? Still a bit unclear then. How is Bitcoin at 13-18k USD/Bitcoin and Bitcoin cash is only around 2.5-3k USD/Bitcoin Cash? So will we ultimately have 21 million Bitcoin and Bitcoin cash is a fraction of it?

It's a very basic question - I'm sorry if it's too rudimentary, but please do expand.
Bitcoin Cash is a seperate fork, a seperate entity. 

There will be (a bit less than) 21 million BTC, and (a bit less than) 21 million BCH.

Price differentiation is because of supply / demand for Bitcoin Cash. 

You should see Bitcoin Cash as an altcoin, and not something that is in any way connected to Bitcoin.