Where to begin – potential sub-division

Hi,

I'm seeking expertise and guidance from those "in the know".

We bought our first and only house in Windsor, QLD, back in 2007, as an investment whilst we were living abroad. We've since returned to Aus and are now living in said property. 445sqm, with 22m frontage, city views from rear. The house as it stands (post-war, highset) is not sufficient for our family size or personal style so we would like to explore our options:

1. Raise, build under, and renovate

2. Demolish and re-build family home for own occupancy

3. Sub-divide and build 2 x town houses, 3 bed 2.5 bath, perhaps sell one, hold other for rental income (LMR, DCP, LURC) – other developments/renos already done on our street and surrounding areas, and our lot had sub-division approvals in place at time of our purchase.

4. Just sell

Where do we begin in exploring cost options for each; for calculating and comparing profit margins for options 3 and 4. Who should we/do we need to talk to for each or all of the options? Do we need to have plans designed fully before they can be costed or are there industry averages? Is it like a jigsaw pizzle and i will need info from a variety of sources to examine the big picture? Basically how do we begin and how much time do we need to allow to get all the facts and figures before us?

Insight much appreciated.