Depth would depend on the weight of the house, house design, number of Piles and as Piles into clay subsoil rely on Friction for their stability the circumference of the Piles. I have in the past built two similar size houses on clay, one had 32 Piles the other only 11. You would need a Foundation designer to specify what would be suitable for you.Would u know how far down the concrete piles should go down for a bungalow going on rice paddy. If I raise the dirt with fill then pile drive supports do I need to wait for dirt to settle?
If using Piles I see no reason why work cannot start as soon as the Back Fill is in place as the structure will not be sitting on the Back Fill, the movement of the Drilling/Driving Rig around the site will help to compact the soil for the later construction of Paths/Driveways/Patios etc.
Again the above info is based on my experience in the UK, I see many successful builds using the traditional Column and Pad design and I am sure the builders on this Forum will have gained a better knowledge than me for Thai house construction, as you are building a Bungalow this may be the best method for you.