Actually, you are doing the absolute best thing you can with any game; you are playing through and learning from your mistakes. Try to avoid the walkthroughs and such as much as possible, since they will lessen your enjoyment of the game. After the first time finishing the game, then go back, read what you missed, then the next game through go back and do the stuff you missed. Other than the quests involving the main plot, the other stuff is all optional.
You can have any party you want. It doesn't matter at all if you keep the original characters, though they do tend to have a large amount of dialog (all optional). I would use a well-rounded party at the very least (at least one each of warrior, priest, thief, and mage), at least until you finish the game the first time.
Your best bet is to read
this site for more information. It is a non-spoiler guide to the game written by one of the experts on the game that frequents this board. It is designed for newbies just like you.