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?
Missing gear has never been a worry for me. The game floods you with so much loot no matter what you do.
There is serious FOMO with story decisions, though. There are certain paths that can cause companions to permanently die or leave the party, cause entire factions to aggro on you at once, or kill off important NPCs. Some of these decisions also hinge on die rolls. You have to be prepared to let it go or embrace the save scum.