First steps of a young four-person family

Hello dear house-building community,
I would like to briefly introduce myself at the beginning.
My girlfriend (30) and I (29) currently live with 2 small children (2 years and 7 months) in beautiful Berlin in a three-room apartment.
We are both permanently employed (she is a special education teacher, I am a chemist) and a few weeks ago we made the final decision to have a small but nice house built/bought (already here the first question).
The rent prices for a four-room apartment that we would like here in northern Berlin (Pankow/Weißensee) would be at least €1500 cold. After some back and forth it was clear that we do not want to put up with that and instead want to acquire something "of our own."
Our dream idea is to find something in the northernmost part of Berlin (Karow, Buch, ...) 5 rooms, 2 bathrooms, at least 110m² living space and a small but nice garden at the back where the kids can play, splash, and climb. And where the parents can sunbathe and, as German as it sounds, of course grill.

Unfortunately, we have absolutely no point of contact, neither among friends nor family, who own a home and can support us with initial questions. So now here is my attempt to get some input from you.

We already had a conversation with a financial advisor. The gist is that with the current salary situation we could finance a house costing about €550,000 (with land transfer tax, notary fees etc. we would be at a total sum of about €650,000). When I search the known portals like immonet, ImmobilienScout etc., it is already difficult to get something decent for this amount. What other possibilities are there to get existing properties? I think that the properties that have already been listed on immonet for some time are not the best...

Several times there are also offers for planned properties. Now my question would be whether someone can roughly check what additional costs come on top for the final, move-in-ready state.

I know it is not possible to name exact sums. But maybe it is possible that someone takes a quick look and estimates what will be added on top of the purchase price.
Feel free to also share your opinions on such prefabricated houses. Since we unfortunately have no experience with construction projects and also no friends or family who know their way around, "building ourselves" is off the table.
Therefore there is only the option of a prefab house or existing property.

I hope you can help me a little.

Thanks and best regards

You are also welcome to share your opinions on such prefab houses. Since we unfortunately have no experience with construction projects and no friends or family who are knowledgeable, "building yourself" is out of the question. Therefore, the only options are prefab house or existing property.

Prefab house = turnkey? -> until the "finished" stage is reached, the builder has to make numerous decisions and ideally accompany the construction (not every day on site but at least check in on all trades). Developer / existing property would be the least work. Can't you ask some coworkers? I’m not familiar with big cities, but I fear that as an ordinary person without connections you don’t get access to the real estate market?

Since we unfortunately have no experience with construction projects and also no friends or family who are knowledgeable, "building yourself" is out of the question. Therefore, the only options are prefabricated house or existing property.

What is meant by "prefabricated house" – timber frame panel or "solid"? I would also include developer properties, as the land would be included right away. Are there preferences: detached, semi-detached, terraced house?

You will need some money for the outdoor areas and the access path to the house. You can achieve quite a lot with just a few thousand euros. It is often forgotten what lighting and interior furnishings entail - here too, you can be very economical and manage with less than €1000 by moving a lot of items along and doing inexpensive temporary solutions - more demanding people will consider this "impossible." It is also advisable to keep some reserve, as something can always break - even if it is just a washing machine that breaks down during the move. Probably the largest item is what is not included in the prefabricated house price. You have to read very carefully here. Rule: Nothing is taken for granted. When buying an existing property, it is better to take a professional along to check the building fabric. For this, somewhat larger reserves are sensible because if you are unlucky, the heating could break down or something else.

When buying an existing property, it is better to take a professional along

With existing properties, I recommend – also to avoid tiring yourself with disappointed hopes – a strictly enforced narrow search filter (and for laypeople in the sense of awkward beginners especially a limitation on the age, to a maximum of 20 years).

Thanks in advance for your answers.

By prefabricated house I meant the off-the-shelf houses. I assumed that you pay an amount X and after a certain time the house is ready and finished. But I was probably wrong here.

We first need to clarify what possibilities there are.

[*]Existing property
[*]Buy land and then have a construction company build a house on it
[*]Developer project (?) In this case it would be a kind of complete package, meaning house and land?

Regarding 1.) I think there is not much to say, as it is relatively clear.

Regarding 2.):

My first research showed that there are developed plots of land with 440m² for €250,000 in the area that interests us. Additionally, there are €38,000 incidental costs, which would make a total cost of €288,000 for the land.

Of the €650,000 "budget" I mentioned, there would then be just under €370,000 left for the house construction.

Here 2 questions: Are 440m² enough for a house and garden + carport? Are €370,000 enough to have a house built?

Do you buy the land and then contact construction companies or is it done together?

Regarding 3.) How do I come across the mentioned developer projects? And what exactly are they?

Thanks and best regards