Wow that's a lot! You should be set for a very long time. Not sure what they mean by guaranteeing them, though. Unless they mean they guarantee they won't be a dud. Cartos are considered disposable (meaning they are meant to be used once and pitched). Granted most people keep refilling them, and as long as you keep them wet, they will often last through several (re)fills.
Finding a juice you like is just trial and error. I have a few favorites (Velvet Vapors butterscotch and velvet vanilla) and also FSUSA butterscotch flavors (ie: hopscotch, butterscotch almond, etc). I just got an order from Honeyville Vapor and the blueberry muffin and waffle are great (even better when combined) and their tiramisu and apple pie are good too. You may find that flavors you enjoy eating, you don't like vaping (and the reverse). I love fruit flavors, but that blueberry muffin is the first fruit flavor I have found that I like. Enjoy!