No, you can create those characters at the start of the game. It is fairly intuitive.
I will say however, that a big part of the appeal of this game is the NPCs and the NPC interactions, particularly in BG 2, where many of the quests are linked to NPC companions. So I'd STRONGLY that a beginner starts a 'normal' game with a single character.
The game is good enough to justify multiple runs, you can always try a custom party later, though if you are anything like me, you wouldn't want to after you've met the ingame NPC companions. Trust me on this matter, I came into Baldur's Gate from Avernum 3, and I too wanted to create a custom party. Somebody back then gave me much the same advice I am giving you now. I've not looked back since...
I'll often create two characters, and recruit the rest. Kind of the best of both worlds, I get to create multiple characters to my liking, and still enjoy much of the flavor of the game.
If you create a multiplayer game I recommend that you move the savegame to the single player folder afterwards - that way you avoid the very annoying pause delays that multiplayer comes with.
Comments
I will say however, that a big part of the appeal of this game is the NPCs and the NPC interactions, particularly in BG 2, where many of the quests are linked to NPC companions. So I'd STRONGLY that a beginner starts a 'normal' game with a single character.
The game is good enough to justify multiple runs, you can always try a custom party later, though if you are anything like me, you wouldn't want to after you've met the ingame NPC companions. Trust me on this matter, I came into Baldur's Gate from Avernum 3, and I too wanted to create a custom party. Somebody back then gave me much the same advice I am giving you now. I've not looked back since...
One compromise you can make is to play with NPCs and use eekeeper to change them to the classes you like.