@Wriggle
1. Yuugi
(Duh, of course! XD), Mokou, Suika, Marisa, Ichirin/Unzan (Unzan, out of those two).
2. This one is kind of hard, but there are songs that I listen to more than others, so here it goes. It's not in any specific order.
Heian Alien, Necrofantasia, Solar Sect of Mystic Wisdom, Emotional Skyscraper, and Faith is for The Transient People
3. This one is tough, considering that after a little bit of Touhou, my eyes feel like their melting from my skull. :p I can't really answer this one.
4. This one is a hard one because I carer for virtually all the canon characters. For me, when I read about them and discover their past, personality, hardships, and he like, I develop an appreciation for them, kind of like with John, Isaac, and Six. Instead, I'll just list Fanon that I like.
Spoiler
Chen: Need I say more? :p

Yukari: So many gaps, so many ways to abuse them and/or troll people with them. :p
Yuyuko: I find it comical how people always depict Yuyuko to be this bottomless pit, and how she can eat anything and everything.

http://fc06.deviantart.net/fs70/f/2010/284/9/1/yuyuko_eats_the_world_by_raocow-d30jaim.jpg
Cirno: Cirno is the Beloved Tomboyish Girl we all know and love. Not too bright, but makes up for it by being THE STRONGEST!!!
Marisa: She steals EVERYTHING; your money, your pants, and YOUR VIRGINITY, all in one fell swoop! XD If it's not bolted down, it's gone. It will be placed in her house, where you will never see it again. There's also the shrooms, but that's just because it's funny to think that her magic is powered by getting high and shooting laser rainbows at people. :p 5. It's a long one.
Spoiler
Yukari: In any given situation, intelligence is an incredibly important trait. Intelligence is and incredibly powerful tool and is the most versatile out of all the traits a person can have. Intelligence got humans where they are today and has proven itself to be a trait more powerful, more useful than speed, strength, or even fighting ability. Being able to plan out strategies and think 100 steps ahead of everyone else is very important for any given situation, and because of that, she would be a valuable asset.
Nitori: Again, intelligence comes into play here as well, only instead of planning, engineering is her specialty. She may not have her powers, but intelligence is not one of them. It's an inherent trait. She would be able to turn even garbage into tools to help us live, weapons to help us fight for our lives, and armor to protect us from zombie bites and scratches. She would be able to make things that no one would really think possible, a MacGyver in a little girl's body.
Youmu: She may be small, but her swords will put you down to her eye level if you meet the business end of her swords. No, she can't swing her sword at 1/4 the speed of light, but her swordsmanship is quite possibly the best in Gensokyo. In a zombie apocalypse, that would be invaluable, the ability to slice zombies down, the ability to easily defend herself and others.
Minoriko Aki: She's not a fighter, but she is a very skilled farmer. In fact, she's the goddess of the harvest, so she's bound to know a thing or two about how to grow food. If that's the case, then we would be able to sustain ourselves when the food supply runs out in the city. She could even teach us how to farm, and then we're all self-sustaining survivors.
Yoshika She may essentially be a zombie, but she's on our side. Because of the fact that she's basically a zombie, the other zombies will pay no mind to her during supply runs, or any other mission that would require her to venture out into the zombie infested area. She would be able to perform tasks one of us could do, walk right into the middle of a horde and be absolutely safe. She may be slow, but she would always be guaranteed to come back safely. Because of that, she would prove to be incredibly invaluable.