Site Costs Jindalee WA

I have purchased a 665m2 block of land in Jindalee in WA. The block is level, sand based and the necessary retaining walls are in place. (constructed by the developer). Aside from a small amount of concrete waste dumped on the block (cement mixer load), the block is clean.
I have been provided with a comprehensive pre contract quote for "site" works which includes pricing not only for earthworks but everything else applicable to building on the block. Some of the prices quoted seem to be reasonable others not so. Happy to pay a fair price and also mindful of not complicating the build process.

For example $3200 - remove vegetation, level and compact. If I were to arrange to have the earthworks done myself (by earthworks business), can I reasonably expect to obtain the relevant certification that will satisfy the builder that the work has been done to the required standard?

$2600 for 2 x concrete pumps (during construction of 2 storey house)

$3450 - corrosion zone 5 (approx 300m from coast line)

$8440 BAL 12.5 (Bushfire Attack Level).

$3600 - 2 x 1500 x 1500 plumbed soak wells

thanks in advance for any advice

Mark

I just got a quote from Perth Soakwells for soakwell installation if this helps. Have heard good reviews about them too.