Is clinker recommended after construction when done by oneself?

I also advocate for it, but most people do it because it probably relieves the most.

Can it generally be recommended to buy a house with only plaster and then hire a company yourself afterwards, or does that result in additional costs overall?

Regarding question 1: I would even say it can rather be generally recommended to discard this idea.
Regarding question 2: that not only results in additional costs:

IMHO a two-shell construction method should be planned from the start (foundation of the facing wall, [...]
Doing something like that afterwards is likely to cause considerable extra effort and often only possible with compromises.

If this decorative shell is "retrofitted," we will practically be talking more about cladding bricks.

Apart from that, your exterior wall will already have to meet the requirements (Energy Saving Ordinance or KfW) in the "first construction phase."

Build your house with the exterior wall that you can afford "in one go." Besides, clinker bricks do not make a house more beautiful, just different: botched compositional forms or proportions cannot be fixed with them – conversely, the same applies, i.e., with a planner who has an aesthetic sense, even a house with a plaster facade does not look like a "cost-saving frame."

A quick question, if I may.

Is this type of wall construction acceptable?

It is from the construction description of my builder.

So the insulation values look good. From a feeling standpoint, 150mm is thin. But if the statics allow it... Just remember this when drilling sometime.

Honestly, the jointing bothers me. Offers [Klinker] and doesn’t finish it properly.

: You have to decide for yourself whether it is okay. The additional insulation is inexpensive and also has disadvantages (fire protection, pollutants, etc.). We have decided on the monolithic construction method.

I thank everyone who gave advice with their responses. In summary, I am classifying the idea as rejected. We will have the planner calculate the brick version compared to the plaster facade with stylish color elements.