Player Account Registration for Mobile Platforms and Browser

Bare with me here as I'm writing this 4 in the morning :D

This is probably my biggest "Where do I start?" question, so there's the head's up.

I have some experience in website development and I trying to see what would be the best approach in setting up a player registration system for games for mobile platforms that will also work on a browser (or vice-versa). I want something basic where the player will sign in and the player's information is store into a database, (name, password, email address, and a couple of variables such as scores). What is the easiest way to do this? MySQL, and if so, where can I find assistance in setting up my game (or even setting up an account system for my site) to communicate with my MySQL that will work with Unity?

I want to later expand on this so that the player can buy additional content for within the game (like a Cash Shop) which I also need guidance in setting up. What is the best way to get the player to get what they buy, maybe having tokens are added to there account that they can spend?

As far as references, buddyrush.sollmo.com and www.blurst.com are pretty close examples to what I am looking for.

Any advice would be much appreciated!