Q1 - yeah, it's just the rules in the DMG; especially as a starting point.
Miners, or heck even a Crafter can slowly get infinite moolah.
TML posted a limiter of 80 to 88 gp, a few pages back ... umm ... just ignore that too
Mercantile feat on only one commoner, blows that up immediately.
So it's kinda a hard fast limit - and then it's not.
Macaulay Culkin does look a little like Pun-Pun at that age ...