Estimation of semi-detached house construction costs

Good evening everyone,
I have been following here for some time. Now I also have a question for you or rather would like to hear your opinion.
My husband and I have bought a plot for a semi-detached house in a new development area. Development costs and surveying costs of the plot are included in the price.
We would like to build two stories. Without a basement, on the ground floor an office or bedroom for old age, a small bathroom, open kitchen and living area, small pantry and storage room. On the upper floor 2 children's rooms, bedroom with dressing room and bathroom. Approx. 140 m2.
We have already received 2 preliminary drafts from an architect and he said it would be doable for €300,000. But I am very uncertain about that. We have already spoken with 2 other architects and they said we can expect €3000-3500/m2 of living space. Those are big differences. What do you think? We are building in the Stuttgart area (but definitely in the countryside :)) oh, and we are doing quite a bit ourselves:
laying tiles, flooring, painting, connecting sanitary fittings, installing interior doors

Looking forward to your opinions!

2000 euros per m2 is a good value. With 300,000 you can make it. But then also consider additional costs etc.

The size specifications are making me pause... We have a semi-detached house with roughly 7x12 = 84 sqm of floor space, and I just don’t see how we could enlarge the utility room into the bedroom + the guest WC into the bathroom on the ground floor without ending up with a tiny living/dining room. And you wanted a pantry/storage room as well. Upstairs it fits better, there we also have the rooms you wanted. Then we still have a room under the roof + some storage space + a small room for heating/ventilation. Where are you planning to put your heating, and the room for the washing machine? About the price - we landed a bit over 2000/sqm, but far from 3000. With zero own work. With all taxes and fees, without garage and outdoor facilities.

What your house looks like also depends a bit on the [Doppelhauspartner], right? Is there one already?

that one doesn't exist yet. The property has not been sold yet. But the purchase contract only states that we must have the same roof pitch and tile color. The rest doesn't matter at all.

Technology, storage room, etc. should be placed under the roof. Storage room and pantry together are only 5-6m2 in total (so not huge :)) Thanks for your information! That reassures me a bit.