Update

On Monday we came to the following overall breakdown of the 5 million square meters:

• Assume that there are 100,000 people working and living on our site. There will be some overlap between these groups - i.e. some people will be both working and living there. But there will also be some people who live there but work elsewhere, and some people who work there but live elsewhere. But I guess that it would be safe to assume that most of the 100,000 people who are living there will be working either within our site or close by somewhere in the CBD. This may affect how you approach the issue of parking. 
• For office, we can assume 20m2 per person. So for 100,000 people, we get 2 million square meters of office. You can assume that office space is fully air-conditioned. A key challenge will be daylight - how to make sure that offices get reasonable daylight.
• For living, we will need to break down the remaining 3 million square meters into 1) residential, and 2) other activities (shopping, recreation, etc). 
• In order to get some idea about the amount of space required for the other activities, we need to know the number of households. The current average for Singapore is 3.5 people per household, so that is 28,571 households. Lets round it up to 30,000 (since the overall trend is that households are getting smaller). Based on 30,000 households we can use Belinda's paper to calculate that we need about 0.2 million square meters. You need to think where to put this space - and how it relates to residential and office spaces.
• This leaves 2.8 million square meters for residential.  So if we assume 30,000 households, then we get 93 m2 per household. Note that this includes common circulation and any other common spaces in addition to the size of the actual flat. I am not sure what the percentage is - but lets say it around 14% - then we get the average floor area of the flat to be about 80 m2 for 3.5 people, which is about 23 m2 per person. This sounds reasonable. Note that this does not mean that all flats should be 80 m2 - there may be a mixture if different sizes. You can assume that the residential will be naturally ventilated, with AC being used only when it gets too hot.