I would start by selecting one of the characters and playing through their story while doing their quest. It doesn't matter which one you choose, but I recommend Kendal since his quest is easily the most annoying because of the three parts to the Book of Truth. You should be able to join my game to make the quest part faster, but I'm not sure if it works (since it's been a long time since I did them). I also recommend trying to find someone that has Extreme mode unlocked so you can beat Encablossa on their game for "The Timid Developer" achievement. Unfortunately I can't help with that achievement since I don't have Extreme, and my weapons won't be good enough for that.
Yeah that item is pretty prevalent. Plus, if you start a new game (with a different character) the collection items stack so you should be fine. The ones to take care on are the more unique items that you get from specific bosses/areas. They are the ones that screwed me.