Developer's retaining wall and New home adices

Dear all friends, I will be starting buiding in Melbourne's Northern new estate in Donnybrook. I only noticed the area is full of underground rocks until I talked to plumbing contractors. This resulted site classification "P" with "H1" underlying site reactivity. Site cost for such site condition costs additional 15k-20k for a double story. Please consider this when signing contracts.

I need your guidance on the following:
1. The developer constructed retaining wall at the back about 1.2m high, but there was no agi pipes. The developer confirmed no agi piples will be installed. Does this comply with AS or relevant building codes? Any suggestion how should we approach this issue? (Please refer to below for a picture of retaining wall)
2.The construction will start in 1 month time. I will get an independent building inspector to inspect four stages. Do you have any other suggestion for me? I am happy to hear anything, for example: inspect the site every week to make sure no rubbish is dumped on site.
3.The backyard will be about 6m x 14m. Landscaping will be done after handover. Is there anything I should do now to make future landscaping easier?
4.The builder will concrete both sides of the house. I want to fully concrete for one side, but leave 50cm natural strip for the other side. Do you have any recommendation how side should be concreted?
5. Any other general feedback is highly appreciated.
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