Initial ideas for building a small house on a backlot

First of all, thanks for answering my questions. That means you would need 27-30m of cables for the supply. So at least 30,000€.

And what exactly does that mean? Only bungalow or multi-story Max. 500m2

One full storey. Finished attic is allowed, as long as it is not then considered a full storey.
Look at the neighboring buildings.
If I were you, I would ask the neighbor above you about the supply, he just went through the whole procedure according to Google.

And what exactly does that mean? Only bungalow or multi-story max. 500m2

A full storey is not hard to understand. It means 1 (in words: ONE) full storey. The attic is defined according to the state building code. In NRW, for example: Full storeys are [B]above-ground storeys that have a clear height of at least 2.30 m. A storey is only a full storey if it has the height mentioned in sentence 1 over more than three quarters of the floor area of the storey below it. [/B] According to the floor area ratio, 30% of the plot area can be built on – this is not only the house but also, for example, a garage. Ancillary buildings can cause the floor area ratio to be exceeded. This can vary depending on the federal state. So no, neither multi-storey nor 500 sqm.

According to the internet, fast and cheap. We live in a very expensive apartment, so we can't afford a double burden for long.

The house is indeed erected quickly, but usually you wait a long time for the installation date. The base plate or cellar is made on site anyway. The interior construction is mostly done on site. Some manufacturers have a bit more prefabrication here, e.g. Schwörerhaus. Schwörerhaus in particular still has a backlog of old orders and corresponding waiting times. On the other hand, with a well-organized solid builder, you can move in six months after groundbreaking. If it needs to go fast, I would not ignore the topic of building permits either. If you have a development plan, you can also start with a release. Large organizations always want a "proper" building permit because they don’t want to take the risk that the contract architect has misread the development plan.

So no, neither multi-story nor 500sqm.

okay, thanks for the clarification. The houses around are all 3 stories, that's why I was confused.
so 150m2 = house plus garage plus garden shed?

First of all, thanks for answering my questions. That means you would need 27-30m of cables for the development. So at least 30000€.

You can find out these amounts quite precisely from your suppliers. Call or check their websites. I find 30000 very high estimated. You are building new and everything can go into one trench. If you are physically fit, you can dig it yourself. That way you save as well. 30 m also do not necessarily require a transfer shaft on the property. We have just over 30 m for water and electricity, but both are connected in the utility room. Sometimes you can also talk to them.

kay, thanks for the clarification. The houses around are all 3 storeys,

A development plan or the building code does not refer to storeys, but to floors. And explained it quite well.