-chan = suffix used for children, people younger than you, or close friends.
-san = standard Japanese name suffix, shows politeness. Yes, using "Mr." too is redundant. Nobody said Yuki is fluent in English.
nekonyunyu = catmeowmeow
You can see a prototype for the "Sad girl in snow" drawing in FredArt, though the actual drawing turns up later on in MegaTokyo.
Yes, that's the popular Japanese snack Pocky she's eating. There's the box on the monitor.
tinami.com is a real website, but what about piroart.net in real life?

Piro speaks:
I already own it.