Dry stone/rock existing foundation, on a slope - suitable for earthbag?

Hello Permies, would like to get your input please.
We are planning to start our earthbag project next month. We are in South India.
While deciding on the specific site, we found an existing foundation/platform that was made by the previous land owner, and we thought we could use that instead of making a new foundation from scratch. But now we're not sure.

The foundation is:
1. Rectangular shape, 4.5m x 9m
2. On a slope, so the front part has around 1m hight of stone wall visible, while the back part is roughly level to the ground.
3. Made of dry stone, no cement/mortar, and looks like a retaining wall. The middle portion is filled with soil and now overgrown with trees and plants.
4. The foundation has existed for at least 15 years, and it's still looking strong. The shape looks fine, and the stones are still in place. (We think that previous owner had built a natural building that has completely degraded since, as we've found no remains of construction, only this foundation).

Questions:
1. Being the foundation is a rectangular shape, is it advisable to make a round earth bag of 4.5m diameter? We thought of making foundation for the circle shape, inside/overlapping with the existing foundation. Reasons being: a 4.5m diameter building is a smaller project for us, hopefully will be easier, and a round shape should be simpler to make than a rectangle/square.
2. How will we 'attach' the first course of bags to the stone? would the regular barb wire method be enough?
3. Can we start the first course above ground, and not inside within the trench, so there will be no toe hold?
3. If we dig inside the foundation, would we undermine the integrity of the foundation, seeing that its dry rock? I guess we'd have to do try..

Would appreciate any inputs. If this foundation is not suitable, we'd have to let go of this idea and start fresh. We'd like to make this work since our land is on a slope and with not much flat areas, so if this flat platform is usable, it would help jumpstart the project.

Attaching some pictures below for reference. Thanks!

I would lay the earth bags directly on the existing foundations.
They appear to be solid, and a circular bag wall would move since its not sitting on enough foundation.
Sure it will be bigger as a rectangle, and take longer to lay up, but altering that foundation will take time and different materials anyway.

I suggest more research of this site and others to get a deeper understanding of building in bags.
What type of floor are you hoping to use?
What is the purpose of the structure?
What type of soil do you have?
Are there plenty of more stones?

You say it looks something like this... so the picture is not your foundation? We really need a photo of your actual site to give best advice.

I would agree to follow the existing foundation for the base of the earthbag walls. If it is as rough as this picture, you will have no issues with the bags shifting. You might gradually curve the corners in to make a more oval shape by the time you reach the top of the walls, if you are concerned about stability. Maybe buttresses or a dividing wall across the middle of the long sides would be helpful. Your roof would need to overhang enough to protect the base. How tall are you planning to build the walls, and how thick will the walls be? What sort of roof are you planning?