Several questions at once:
Why does he need gold? From the point of view of lore, not from the point of view of game mechanics (everything is clear there).

How will the main character, the cleric of Jergal, go mad when he finds out who is traveling with him?

When we find out the truth, it would be good to find out his real level and the amount of hp, as well as change the character's name to the present.

Why would he travel with us? This is another question, the answer to which will be in the second act.