Very interesting read brendio. I have a possible 29 lot subdivision coming up and your thread is very insightful.
I hope my threads help you in some way in your venture, should it materialise.
We had quite a wet weekend, although not as intensely heavy as last week. Even so, it was enough to cause a bit more erosion above the stormwater pipe where there is no grass cover yet.
I have arranged for a quote for raising and lowering Telstra pits to the finished surface level for our new concrete footpath. This is an additional cost we had not factored. Compensating this, we were able to avoid needing to replace a section of water main that council were requiring and for which we had already paid them, so we will get some money back from that.
I need to sit down and calculate the costs remaining, but we are generally on budget within the contingencies we allowed. The lesson is that you do need to allow for contingencies that will inevitably crop up, and when you have a smooth run, the unused contingency can add to your bottom line. It's nicer to have a positive surprise than a negative one.