Construction Costs SQM Rate Townhouse Project

That is great to find out the rough costs for a custom build.
You have to remember to factor in elements that are unique to your site that play a big part in the build like footing costs. As you are doing a feasibility it is up to you how much money you invest to see if it is feasible. If you are building I would say you would want to get a soil report before you purchase the site. If there is uncontrolled fill or highly reactive soil this can blow your profit out of the water real quick.
Those calculators are okay for a 5minute feaso but I think you want to have stronger figures that are specific to your site and house designs before you take it seriously.