Multi-family house: arrangement of residential units, trees, etc.

Yes, you are right, but I was under the impression that a [GU] has a permanently employed architect and planner and that they are not paid according to the price of the house.

Is the fee for architects fixed according to [HOAI] or is there also the possibility to negotiate if the project is larger?

Yes, you are right there, but I was under the impression that a general contractor has a permanently employed architect and planner and that they are not paid according to the price of the house.

It may be that large general contractors have their own architects. If they then receive their "small" fixed salary, more profit remains for the general contractor :)

Is the fee for architects fixed according to HOAI or is there also the possibility to negotiate if the project is larger?

HOAI is already the basis; however, within HOAI there is quite some room to maneuver (fee zone, minimum/maximum rate), so that it is enjoyable for both parties.

Can someone recommend a good architect in the Hamburg area?

Can someone recommend a good architect in the Hamburg area?

You can find this question under the title:
Multi-family house, trees and such...

Maybe start your own thread (it doesn’t hurt) or look in the Yellow Pages. Hamburg with its surrounding area within about a 50 km radius is full of architects.
You should look for one who can also realize your house style, possibly has references for it.
Because what good is a GOOD name now if they specialize in Bauhaus style, but you want a captain’s gable with thatched roof?
Drive around the area and talk to builders about whom they used. In new development areas, there are always signs as well.
A regional search is more valuable than a nationwide one in a forum ;)