Michael
I would like to comment on your statement below that your costs to develop should not rise by more than CPI.
I think this is a large risk area you might be overlooking. I worked and owned a business in the building industry for a long time (20 years).
As you might know the building industry (material and labor) is cyclical and the cycles depend on things like the economy, demand and supply equation of material and labor among others.
Eg: Government policies do not encourage employment of apprentices (decreasing subsidies to employers), 4 - 6 years later theres a shortage of tradesman. If that coincides with even a small spike in demand, prices will go through the roof.
This has happened in the few years previous but i've seen it more pronounced over my time in the industry. (which i'm not part of these days)
A similar thing can happen with material. Eg: Price of copper has increased substantially in the last couple of years with the resource boom and there fore electricians and plumbers quotes have risen accordingly. (as you can imagine they use a lot of copper)
These are just a couple examples of many that can affect cycles in the building industry and you should be aware that it has nothing to do with the CPI.
If peak building industry prices coincide with depressed property market it could be a very dangerous time for you to develop. Especially considering the development/building time frame can be up to 2 years (or more).
BTW: I used to know a small developer (attached duplexes) that operated in Western Sydney that was caught out exactly this way and went under.
His margins were too skinny to handle the increase in tradesmans rates and material prices. But the margins were considered standard for a spec builder/developer.
Mate, hope it all works out for you and there are that many variables hiding risk in the development world you cant cover them all. Just something to keep in mind.
The cost to develop it shouldn't rise above inflation, so I'm happy to sit on my DA for a while and not rush it.