While it is a great game, I'm not sure, with the questions you ask here, that it's the type of game you are looking for.
Overall, it has a very good storyline with believably real character personalities. But most of the story doesn't relate to the main plot. The game spends about 10 minutes establishing the basics of what your quest is, then the next 20 hours or so doing small side-stories (almost like TV episodes). You're travelling from town to town, and you pick up a few new teammates with a similar goal, but you don't catch up with your target or find out what he's actually up to. Heck, one of the main premises of the back story (that the entire castle population got turned to plants except for the nameless Hero, who was mysteriously immune) doesn't even get explained in the main story; you have to beat the game to unlock an extra area and go in there to find out what the deal was with that.
There are a few love stories (Hero and the horse...er Princess, Yangus and Red, Angelo and any female he comes across), but they aren't really central to the plot. Hero's is important for the final cutscene, and is used a few places for little breaks in the action. Yangus' is important for one of the sidestory "episodes", but never again after that.
And one final thing to note: Dragon Quest VIII is a bit goofy. The entire series is, as they've never taken themselves seriously.