Respect for @ . Anyone who drags through 172 posts and still responds has endurance. Others would have given up long ago.
Incidentally, I still agree with the consensus. This is tight, not to say too tight. I miss the buffer there. "There's still room," "I'll do that myself," and "I'll do that later" are some of the fundamental evils of uncertain planning ...
However, I have actually seen few construction projects (=0) where everything is 100% set by the move-in date. Garage, garden, terrace, etc.... These are things that, I would say, most (at least as I know it) carry out gradually in the EL.
Regarding the EL: what is problematic about deliberately planning something as EL that you or your family do professionally?! I see it as important not to overestimate yourself, so the planning including the scheduling must be very precise, yes. And who does what and to what extent must also be certain.
About the buffer: yes, additional costs will come. The question is, how much buffer do we still have to add to feel safe. We were told by the already frequently mentioned friends that 20K as a total extra was mentioned. Saving 20K I see as quite realistic. If 50-100K is estimated, it becomes impossible. Then the question also arises as to what exactly for? And unfortunately, not everyone who contributes here provides an answer to this question.