If your building a retaining wall over 1mtr high in brisbane , you will need an enginner to design it, he will take in consideration of the soil type for how deep to make the foundation, and also how much load is on the wall, if any load bearing surcharges are present like vehicles passing ect. Generally block walls will need a toe in the foundation that sticks out from the wall the higher the wall the larger the toe, the closer the steel risers are and thicker they get. The wall will need to be corefilled with cement usually 25mpa if its over 1mtr high, There will need to a sealant painted behind the wall and gravel backfill and a aggpipe drain, It is very important that the drain functions properly, meaning has fall and drains away to a suitable location or into the stormwater drain. We build alot of these walls and timber ones too, if you go to the link you will see heaps of photos under retaining walls brisbane . Here is a link that might be useful: http://www.cpricelandscapes.com

Opinions about concrete vary widely on these forums. Claims of long experience may simply mean that they have been doing it wrong for a long time. Take whatever is posted here and use as a basis for more research that you will do. Concrete is either 1. a slab placed over a supporting substrate, or 2. a component of a bridge. A bridge has reinforcement which supports both all of the components of the bridge plus the loads that the bridge must bear. Cracked floors could indicate an improper substrate. Concrete made from Portland cement shrinks as it cures. Fiber helps to minimize cracking from this cause. Control joints are used to create deliberately weaker places where such cracks can more easily occur, hopefully sparing those areas between the control joints. A poorly-prepared substrate that varies in height, i.e, not level, virtually insures that concrete placed over it will crack where the concrete is thinner. None of my interior concrete has any cracks after 10 years. The basement was solid soil with 4" of crushed stone compacted with plate compactor. Fiber is the only reinforcement there. Part of my garage is filled 8 feet deep. Filled with selected soil and compacted thoroughly with a "jumping jack compactor' every 8" of added soil EXCEPT adjacent to the basement wall which would have put too much lateral pressure against the wall. Then rebar formed a bridge over the deepest fill and wider spaced rebar is over the full garage area. Fiber was used there. I would not expect fiber to provide structural reinforcement. Fiber slightly hinders getting a slick final finish on the concrete. Keeping the concrete CONSTANTLY wet for 30 days will insure much greater strength but does not appreciably affect cracking. My lot is like yours. My yard is graded for water control. House main floor level is lower than the road. A gentle swale is created about 30' from the house and then the yard slopes up to the road from the other side of the swale. The swale slopes downward gently to one side of the lot. No water in the basement as it easily runs away before it gets to the house. The ground level adjacent to the house is about 2' higher than the bottom of the swale at it's highest point. Here is a link that might be useful: Swale

Concrete hardens and becomes strong by a chemical reaction between cement and water called hydration. That reaction is slowed by cold weather so it must be accelerated. What is often mistaken for antifreeze are the chemical admixtures that accelerate the rate of hydration so the desired minimum strength can be reached before the warmth from the heat of hydration drops far enough to stop the chemical reaction or freeze the mix water. There are additional ways to accomplish that task like heating the mix water, using Type III high-early-strength cement, air-entrainment and covering the work after the pour. Formed stem walls retain heat much longer than slabs so slabs need special attention or they should be poured later after the house is enclosed or much later in warmer weather. This is one of the advantages of basements.

It may be impossible to find someone to do it because of the severely limited access, but spraying the walls with shotcrete or gunite reinforced by wire mesh is an option. These very dry forms of concrete sprayed under high pressure will stick well and fill voids, forming a solid wall. Much more likely to last than trying to cast wet concrete into forms.