But if you don't want to believe the claims here that combined transactions of land purchase and house construction are jointly subject to real estate transfer tax, then you should simply be able to buy the land now, especially if it comes from the municipality. 
It no longer comes from the municipality.  
 Apart from the fact that I also find these entanglements concerning based on the information we have...
If I were you, I would go to the municipality and request/obtain a draft purchase agreement for the land purchase. Only when you have seen a purchase agreement draft in writing will you obviously know whether you are really supposed to be contractually bound in writing to construction company X or Y or not!
All further consequences regarding real estate transfer tax or the evaluation of the payment plan have already been explained by previous speakers. 
The municipality cannot issue me a purchase agreement. The entire area was bought by a land company. They are developing almost 32 plots here.
As I said, I don't like this whole behavior either. I am also on the waiting list. At first, they said no problem, then one learns more and more things like those described above.