I haven’t played any Baldur’s Gate games before but I’ve heard so much about this game that I’m going to buy it.
However, before I start, I always wonder about this: some games allow you to unlock any weapon at some point in the game, and if you miss one in some quest you can always go back. If you accidentally sell one you can buy it back or forge a new one again, or have it respawn. If you want some other class you can switch later.
Other games are not like that, and if you screw up or aren’t aware of [full in the blank] then you can’t unlock something.
What’s the story with BG3? Do I need to be careful and plan before going on missions?
There are absolutely irreparable consequences to your actions in this game. You have to “plan ahead” in the sense that you have to be sure what path you want to go down because other paths will become closed or non-existent. It also is sometimes not obvious which path makes the most sense to take, which is by design.
Without trying to spoil anything, I made a mistake with one of my characters which caused them to permanently leave the group and I can’t get them back.