As for how to keep them?
It's actually simple. The lands, mountains and rivers that Jiang Chen took from the Five Elements secret realm are the best habitats for these fierce beasts. He could just throw them there and let them live or die on their own, sparing Jiang Chen the trouble.
Moreover, these lands, mountains and rivers are resources too. Not to mention the innate spiritual herbs, precious ores, divine gold, and innate magic treasures they contain. Even their own characteristics are transformations of the original source of the innate Five Elements.
Once refined, he could obtain a large amount of precious resources. All these treasures are resources that Jiang Chen has prepared in advance to help him breakthrough to the Innate Dao Sovereign in the future.
