Despite joining throughout the first 1/3 of the game gradually your party members join at lv1 so you'll have to grind em up when you get them. You may need to grind the party in general for a fair game but it's not an extreme amount, the exp you get just playing normal is alllllmost enough but you may wanna grind just a level or two for a smoother time. Read the item descriptions and don't just look at the status changes, additional effects are only viewable in the descriptions. The Casey Bat is an infamous example. Also talk to as many NPCs as possible as often as possible. There's a LOT of dialgoue in this game and it's mostly very charming. Otherwise it's a pretty straightforward playthrough.