Now, regardless of the costs which in my opinion won't add up like that:
Imho your critical acquaintances are right.
Why do you want to tie yourself down with a house as a single person now? Unless you are sure that this situation won't change in the next 30 years, it's just nonsense. If you meet a woman, have 1-2 kids, the house is so unsuitable and written off.
It makes no sense to plan a house for a family now, nor does it make sense to build a single house.
You can rent out a condominium well; with single-family homes, it's regularly a loss-making business.
Buy the land, that's your investment, and use the low-interest rates. Then, in a few years when hopefully you know which direction things are going, you can build on it or sell it again.
In the meantime, enjoy your life, take nice vacations, buy yourself a sports car. The seriousness of life will catch up with you soon enough ;).