Gu Cultivation was very similar to the Demon Race because Gu were ranked and the rank of the Gu determined the rank of the Gu Master. Also, different Gu have different requirements in order to tame, raise and use them. All types of Gu exist in the world, from typical Strength Type Gu to Space-Time Type Gu, you just have to find and tame them.
The Gu Dao is also a lax and free path, able to dabble on one or multiple at the same time, only costing you resources to help them grow and evolve but it also had to be remembered that just because you can use any Gu Insect, doesn't mean that you're compatible with it.
Compatibility is also a key factor when cultivating Gu. With a weak and frail body, the Strength Gu can't be fully utilised, with extreme bad luck, the Luck Gu can't be utilised, with Blood Deficiency, the Blood Gu can't be utilised so yes, Gu have to be carefully chosen and be useful to one's path to the top.
