Why is there a hose routing the crank case to the intake?
 

As mentioned in topic.
Can I just put a breather on that crankcase hole and plug that hole on the intake pipe? or is there any reason to keep the crankcase vaccume? Thanks !!!

it sucks pressure from the crank case/valve cover... yes it has a reason. you should buy a catch can if you want to do it right

btw, you have 240 posts haha

As the engine runs, pressure builds up in the crank that has to be vented out. PCV has something to do w/ crank vintalation too I think.