I have reached Sapphire Ridge and gathered more than 400K coins. Usually I just buy sandwiches and sometimes other types of food. Purchasing equipment is not worth it.
Still, if you do lots of quests and exploration, you end up with more money than you can reasonably spend lol. Last playthrough I got to over 1 million at some point
May I ask what made you want to do more than one playthrough? I’m 50 hours into it and I don’t think I’d want to go through the game several times because that’s a lot of hours.