Heads-up, you may want to make two characters: One to progress through the campaign, and one for co-op to play along with someone. The way the quest system works is that if you're on other ends of the quest spectrum, you'll take the higher person's quests, but even if you complete them, the lower person doesn't get those quests counted as "complete," so you'll end up with a lot of wasted effort if one of your goals is to make it through the campaign, then you're kind of stuck unless you're following someone with the exact same quests and progress as you.