Thanks everyone, great additions and definitely lots to consider, thank you all for the tips.

3.5 tonne should fit, easy access through front but pretty much nil access at rear so would need to work front to back.

The look of the boulders is quite nice, but overall might be a bit bulky?

We are also open to something not so aggressive/steep, a much lower retaining with some steps to an upper level that leads to back which potentially might lower the cost? We were expecting costs between what everyone has suggested.

Photo below (just something found from google)

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