Then I'll make a calculation for you that I consider realistic based on today's experience, and then we'll compare it with your desired budget.
House: 240sqm*2000EUR=480k
Double garage: 30k
Additional construction costs: 30k (with level ground and thus low costs for earthworks and low costs for the architect)
Outdoor facilities: 25k (self-performed)
Kitchen and other equipment: 25k
Total: 590k
Your maximum budget: 500k
Even if you try to make the numbers look better and think you can save 90k through self-performance, it's all a tight squeeze from the start. If from the beginning of the planning phase the desired vision and budget don't match, the construction will be a stressful and nerve-racking matter.
In my calculated 590k, there is no buffer at all. No special buffer for unforeseen events or extra wishes during the construction phase. And many nice things will come your way, and saying no every time is not for everyone.
And then realistically consider how you want to do a whole bunch of self-performance with a baby. You would certainly spend your entire vacation, weekends, and any free time on the construction site. I'm not at all of the opinion that it's impossible. But I do believe that with a child it's not feasible (or at least in very rare cases). All young couples without children can do that for a year and focus everything on the common goal of building a house. But such a strict prioritization is, in my opinion, not possible with a child. I'm sure one thing will suffer: the relationship, the child, or both.
So I would advocate setting the priorities precisely and scaling down the build.