I make myself follow a rule of never keeping more than 20 of any item, because I figure I'll rarely ever need more than that at any one time. So after a few quests I always go to the shop and sell anything that exceeds 20. gives me a good chunk of change, and it adds up after a while.
At one point I amassed well over over a 100k haku, but I wasn't buying all the sets, just the ones that I figured were worth getting at the time. I do plan on getting them all eventually just to have them, but probably later.
What's really eating at my haku right now is the shrine that lets you donate up to 9,999 haku, lol. I did that for a while before every battle but it's clearly not sustainable, so I donate a max of 4999 now.