Buy apartment, then buy/exchange house - tips

Of course they exist and for owner-occupied properties the period is just shorter.

That is definitely wrong. Owner-occupied properties are not subject to any speculation tax. Even if you sell after half a year, you can keep the entire profit (if any profit is made at all).
Don't drive the original poster crazy.

The model of continuously buying something new and moving until you live in the right property is widespread in England and usually works. Buyers as well as banks speculate on an increase in the property's value as leverage for the next purchase. Often, the first property is not even paid off, but only the interest is serviced. Whether this is still the case today, I do not know; in the past, there was a mortgage of up to 120% of the purchase price (after all, you also want furnishings...).
At the moment when house prices fall (as most recently in 2008/09 and 2016 in England), the banks realize they have "bad loans" and begin to react nervously. This has nasty consequences for those who have stretched the principle too thin – in GB, there were quite a few in 2008/09, as this was simply common.
It simply depends on how you see the value development of your flat and how far you push yourself for it.
I think your idea has many positives and would probably act that way myself.

Hello, on the one hand the condominium gives you the option that you own property in case it doesn’t work out again. On the other hand, if it does work out, your financial leeway is limited.

Then you have to deal with the following topics:
* Children are there, less income and higher expenses = probably no loan for the house
* Renting out the condominium
* Selling the condominium and interim financing or property change

The condominium would be okay if you want to live in it longer, but moving again in 3-4 years is not good at all. As already mentioned, you will burn a lot of additional purchase costs, possibly also the upgrade, a kitchen that doesn’t fit into the house, etc.

But to ask stupidly... the condo costs 480k€, a loan amount of 400k€ with an income of 5300€ net is certainly in relation. Now you say the plot alone costs 250k€. On that a single-family house, I think we are well beyond a total budget of 600k€. And that makes it tight, especially if there are children and you can even financially manage this house at all. And that is completely independent of the possible purchase of the condo (resulting "losses" would be an additional burden on top). It is seriously a question to ask whether the dream house is generally realistic with your income.

Maybe you will find your answer from this.

Don't do it.
Additional costs too high (not just the purchase ancillary costs, think of furniture, moving, stress, etc.) and you definitely want to build. What do you want in a 4.5-room apartment without children?
By the way, they don't come from Amazon, your supposedly fixed plans and the wink to God's ear, but start with the children first, keep saving capital, and prepare for the allocation of building plots.