Of course, the main inspiration for this story is the Chinese novel Journey to the West, best known in Australia through the TV series Monkey Magic.
I have fond memories of a few stage productions of the story, that took potent inspiration from the book's spiritual themes. The priest Tripitaka's journey to India is not just a physical one, it reflects his own development as he learns to wrangle his internal energies. The monkey mind must be trained to follow orders...
You can even map the characters onto the lower spheres of the Tree of Life in the Kaballah. The lustful and gluttonous Pigsy of course is the lowest sphere of the earthly realm, and unwordly Tripitaka represents the central sphere of spirit. Crafty Monkey neatly slots into the sphere of thought/language. Then depending on your preference, the horse can represent imagination, and Sandy can represent emotion - the approach I've taken in this story.
Of course, there's another layer of symbolism in the book, related to the Chinese cycle of 5 elements, but I can't pretend to understand all of the nuances of that system.
The relevant thing for me is the characters represent common themes in the spiritual journey, irrespective of your formal belief system. Also, all 5 characters are essential parts of the journey - we need our mind and feelings and imagination and body and soul.
From there, I wanted to redeem Pigsy, who is usually the butt of the stories - true, Buddhists want to curb the unchecked desire he represents, but the earthly desires keep us alive, and also represent the nourishing beauty and wonder of the physical world. Each of the 5 characters has to be there, even if (like Sandy and horse) they don't do much, because the more popular characters hog the spotlight.
To illustrate this, I tapped into the Buddhist taboo on meat-eating, which was not firmly fixed in Chinese Buddhism in the period of the story, the early Tang Dynasty (from 618 AD). I try to be mostly vegetarian myself, but wanted to show the complexity of this issue. For example, under Confucian belief the elderly would get more meat, because it was known to be more nourishing. And then there are questions about wasting meat that has been served to you. Right and wrong can be slippery things.
Also, in the book Tripitaka is shown to have huge flaws, such as moments of cowardice and hypocrisy. So it was in keeping with the ironies of the book to show that true virtue is more than just false purity.
I tried to make sure the food was realistic for the location and period. The Emperor's Feast by Jonathan Clements was an invaluable resource, so that I could say on balance of probabilities that they could be eating dumplings and noodles!
Another element that fed the story was my experience of the full novel Journey to the West - excellent stuff, but extremely long, and hugely repetitive, usually with deus ex machina resolutions to conflicts. So my weariness at all of the monster-of-the-week following the same plotline was the basis for Tripitaka's fatigue at the start of the story.
For the ending, I realise it might be jarring for some readers, but I wanted to have that contrast between the adventure story of the book, and the basis for Tripitaka, Xuanzang, who undertook the actual journey from China to India to fetch the scriptures. That tied in nicely with my idea that when all the internal energies are owned and accepted, illusion vanishes. Feed the body, heal the soul.