>>714729320
Finsider Ignis can be found in fishing spots on Feybreak
Celaray Lux can be found in the fishing spots on the island with the Terraria dungeon
Penking Lux can be found in the fishing spot on the third wildlife reserve (the one near the desert)

>>713924951
It's dependent on your Gatherable Objects settings, if you have them respawn as fast as possible and give more items, you get three hearts per crystal and it respawns in seconds.