First of all congratulations on making this decision and progress, i myself bought my first home in Mumbai before 2 years.
I also started searching for a good slightly discounted under construction property. Everytime i used to visit builder, i used to see those miniature models and brochures, hardly few of them had sample flat and you never get to see what would be the ambience of say garden or lobby or etc at that time.
Plus, no matter how big the builder is, there is always a chance and risk of project getting paused or stalled for something or the other reason. Some big builders of Mumbai has projects that are stuck since 5-10 years, generation have also changed in some but no resolution. I am not saying this to scare you but these were my observations.
And last but not least, after a building is completed, it almost takes about another year or so to have the lively ecosystem up and running in that building, like regular guards, maids, cooks, gardeners, etc. People will get their interiors and furniture done, so if you move immediately, you will go through lot of noise and drilling around you.
Looking at all these issues, i purchased a ready to move in new, direct purchased OC received home. I understand it can be hard to find a project like this in certain locations and you dont have an option but to either look for resold 5-7 years old ready to move in properties or find someone who just got possession but is looking to sell immediately.
For point 2 and 3, i am not from Gurgaon so can't help. But best of luck. And congratulations.