If it were because of business, Chinese maybe? Get on with the hardest language so you can learn the easier languages like a piece of cake hehehe! Yes, Chinese is the base language for Korean and Japanese writing so it would be advantageous. But! Since I am more interested in understanding my Japanese friends better as of now, I'll go with Japanese. :)

The really depends. Just pick one and go with it.

Chinese grammar is easier than Japanese and Korean. Japanese pronunciation is easier than Chinese and Korean. Korean is easier to write, with no Chinese characters.

if i need this maybe, but, if really is for the moment not very important, maybe, first, i will look for a beautifull woman of one of these countries, and, if she is korean, then i will begin to study korean,,,,

Chinese because it's very popular right now regarding business. It's also the base for Japanese and Korean if I recall correctly, the writing language anyway.