"El día de hoy" significa en inglés: "the day of today". Es una expresión que no vas a usar cuando hablas sino cuando escribes en un contexto particular.

 

Hoy es más común y es lo que deberías utilizar en la mayoría de los casos.

 

Saludos,

All the above suggestions are good. I would recommend reading something that is neither long nor complex writing by an English speaking author. A cheap/free option is reading online any book that is already part of the public domain (that means it has no more copyright protection as the period has elapsed) and those are classic literature. Also, since you are into Asian culture, take a look at Anna and the King of Siam. There is an excellent movie out there with Jodie Foster. Good, interesting, romantic and historically inclined. I think it is a pretty strong choice.

Both are informal ways of greeting someone. Hi is less formal than hello; hence, being more appropriate to be used in casual situations. In short: "Hi" for friends. "Hello" for anybody else.