As a layperson, I unfortunately cannot provide you with a better assessment of the individual positions, especially for the Frankfurt area. But other forum members, for example [Bauexperte], can certainly help you further.
Experience shows, however, that the 1,700 - 2,000 TEUR per m² is repeatedly reached. Even if [BU A] produces the trade X cheaper than [BU B], trade Y at [BU A] then costs less than at [BU B] ;) In addition, various installations are often underestimated. For example, the bathrooms often end up being more expensive than initially assumed.
I think you can only underbid the positions if you do a lot yourself and tap into all savings potentials (leftover materials, plaster facade instead of clinker, etc.). Friends have done that and actually stayed just below 1,700 TEUR. But who can work six hours every day on site?
But that wasn’t the point anyway ;) I think you should get various offers or obtain calculations from architects and then compare. You will probably find the golden mean somehow. But given your initial situation, I don’t see a problem with the + 20-30 TEUR either.