Thank you very much for the many responses.
Regarding income: No bonus payments etc. have been taken into account in the mentioned net income, as I consider this careless since they can also occasionally disappear. We are therefore only talking about what comes in from our current jobs. My partner's secondary job is not calculated yet either. So we still have some buffer here.
Regarding costs, I agree with you. I think we are still planning a bit more leeway. But kitchen and carport for €50,000 we find quite ambitious. We will probably come out at around €13-14k for the kitchen. An appointment with the kitchen builder has already taken place for early planning.
Other parts like sanitary, electrical etc. will be ordered soon as soon as the plan is finalized. The installation is also already secured. We will probably subcontract the shell construction to a large extent and then carry out significantly more in the area of interior construction ourselves. Especially in the field of electrical work, we have already been able to do a lot ourselves in a previous project (chasing, holes for sockets/connections etc.) and then joint laying with the electrician. The photovoltaics will also run through this, and procurement will be done via my employer (I work for the energy supplier). There are therefore further conditions here.