Well, you can choose to have a shared pool of money or keep separate "wallets", there's a book in the mayor's house that will let you toggle between these options. Another good thing to know is that the elevator in the mines works for everyone, so if you make it to level 40, everyone else can use the elevator to go right to level 40. Also a lot of things are player specific, each player can collect rewards from chests in the mines, from the museum, and all quests are per player, so each person will need to do each step of quests.
I've found fun in having each person get different perks from leveling up to 5 and 10 in respected skills. I play with my girlfriend and we take different routes to give us niche roles as we play. Fishing can be a bit tougher in multiplayer as the clock continues to run as you catch a fish though so watch out for that. Each player can catch the legendary 'hat' fish and get all the stardrops so you don't have to worry about sharing. Honestly the best part of multiplayer though is just working together and playing with your friends. It feels almost exactly like single player aside the fact that you can share the moments with others!