Are the construction costs listed correctly?

We realized an individual plan with a solid house provider, i.e. I have to add the architect and structural engineer fees to your interpolated value and would then come to about 390,000 euros as a comparison value. We are significantly cheaper with 144 sqm of living space on the ground floor and upper floor and about 70 sqm of basement, fully equipped with underfloor heating, KNX cabling on the ground and upper floors as well as a whirlpool and laundry chute in the bathroom.

The slope at the garage will be made with L-shaped stones. The basement is exposed in the rear part due to the slope. No KFW. Solid construction with pumice stone without [WDVS]. Tiles / package / electrical medium standard Basement and ground floor are full floors. Underfloor heating in the ground floor and bathroom upstairs (rest via radiators). Upstairs with a height of 2.30 at 44 degree slope ([Zwischensparrendämmung]).

For us KFW 70, which roughly corresponds to the current energy saving ordinance you have to build according to. Then solid Poroton without ETICS, basement made of waterproof concrete, room height after screed: 2.70 in the ground and upper floor, in the basement 2.35m. Based on the comparative value of 390,000 euros, we are almost cheaper than your architect's fee.

And decentralized ventilation is also included

we build "only" according to the Energy Saving Ordinance, no ventilation will be installed. does it make sense to work with the architect only up to phase 4 and handle the rest independently?

How do you want to carry out the execution planning and tendering on your own? Or rather, no, that doesn't make sense.