Landscape protection area - possibly purchase - many open questions

However, you may be seeing things too negatively here

Yes, maybe. I'm not saying it's impossible. If dog breeding can be portrayed professionally, I do see planning law opportunities.

as you suspect

Originally, the suspicion was mentioned by the OP and I thoughtlessly wrote "illegal construction". I rather suspect that it is a privileged agricultural site, where farming was abandoned many years before the vacancy and the building was still inhabited by the former operators until 2008. The "newer" building is a former farm building that was converted for seasonal workers - hence the temporary residential use. The construction of the garages may also have been permissible under the privilege. For buyers, however, completely different rules apply, starting with the Building Code, the nature conservation laws, up to the Building Energy Act, which must be queried rigorously with the relevant authorities before the purchase.

There are usually good reasons why such properties remain vacant for a long time. And 13 years is extremely long.

We have 6 dogs

That made me think of a business, namely:

possibly Great Dane breeding)

:) That would need to be checked. You might be disappointed, but it will probably open the doors you need ;)

If a property stands empty for so long, it's a "groschengrab". And I would say goodbye to planning everything alone. If the building authority wants to see something, a professional must be brought in, architect, etc. If you have deep pockets, go ahead, if not, leave it...

... possibly Great Dane breeding)

Do I understand correctly that you want to register a business there (or whatever it is called in animal breeding)? Maybe if you add a few chickens, you can find some kind of "niche" as an agricultural operation.

I am really deeply sad because that is exactly how I always wanted to live,

Now try not to be sad for now, it is still much too early to give up. What do you think, which hurdles and difficulties others in this forum had to overcome? First of all, there are only many open questions, as is the case with every house project. And whether they will be decided negatively or positively, neither you nor anyone here knows. Come on, get to work. :)

If I were looking for a niche and owned so many dogs, I would consider the label dog boarding house. We maintained a medieval half-timbered house for over 30 years. It is neither cheap nor fast, nor do the investments last as long as with a stone house. It can still be absolutely great.