Can I Use Earthbag Tubes to Retain the Walls for an Inground Greenhouse?

Hello, I am brand new here and am hoping that someone has some resources on using the earthbag tubes to build a retaining wall for a 12ft wall on the high plains of Colorado. We are looking at building an inground greenhouse, 32'x16' and 12ft deep on North wall and 8ft deep on South wall. We want this to be 100% passive so looking at building a "cooling tunnel" as our entrance in the middle of the structure as well, preferably on the south wall. I should mention that the soil here is heavy clay.

Along the north wall I thought about either cutting in 2ea 3 tiered growing beds during excavation or adding them in after the wall is retained. The base would extend out about 10ft and the top one would sit about 6ft high. They would both be shaped essentially like a half circle to allow for more strength in retaining the earth. I want to do this 1) because it should help the load for retaining the earth where it is stepped and 2) this would allow us to utilize more space for the plants. I don't want to go higher because I am not sure how the temperature fluctuations will be closer to the glazing and roof and I need the upper space to be covered with aluminum to help reflect winter light down to raised beds towards the south wall. I plan on building the walls of the tiers with the earthbag tubes.

Questions:
1) Is this even doable?
2) Is stepping the wall back during excavation enough to be able to use the earthbags or do I need to add rebar or something else to get the strength required?
3) If we cut in the tiered beds, would there be an issue with drainage when (the few times a year) it rains or the snow melts?
4) If the earthbags won't work, is there anything that would be cheaper to use than concrete?

Any and all advice or points to quality resources would be greatly appreciated! If this works out, we plan to put 4 larger ones on the property and be a year-round farm to supplement our egg business (1000+ pasture-raised chickens and we do home-deliveries and our customers love fresh produce). Plus we would have the ability to grow just about anything we want off the grid.    

We built our earthbag house (not tubes) with round walls set underground on the W and N sides about 5 feet.  We used plastic (2 6mil sheets) and cardboard to protect the plastic as we backfilled behind the walls.  You don't want moisture getting into the bags so having growing soil right up against the bags inside might be an issue if the earthbag walls are load bearing.  They might slump.  We also protected the walls with foam board wedged behind down to the frost line.  That protects the walls from the freezing temps that can be in the ground in the winter.  Also exterior drainage earthwork is necessary to make sure water flows away from the structure.

I'm actually thinking about adding cement (my former self is shrieking) to the mix in the earthbags to do an exterior retaining wall for a place where we had leveled by backhoe to put a High Tunnel.  I avoid concrete as much as possible but maybe a soil cement is more stable for places that will have moisture.  Better than concrete block!  I actually just got on this thread to see if anyone has experience with adding cement to earthbags to make them stable for outdoors.  How much cement is necessary, is my question.

Round earthbag walls are super strong and can certainly be retaining walls.  You know the bags themselves will break down in UV if the mud plaster wears off, which is likely to happen with a lot of moisture or outdoors.
Amanda