I also proceeded in two stages - having lost my GÜ-Sanis. First, I checked who was even available, then informally contacted them with a rough description of what it was about and whether there was any interest and capacity, and for those who showed interest, I then sent out the tender with a request for an offer. In the end, I had three genuine offers. In the first step, I had contacted well over 10, closer to 20. The winner was the one who from the start expressed his interest but at the same time honestly warned that it could take longer timewise, but then was very committed. Coincidentally also the cheapest, which was just the cherry on the cake. If the price had been the same as the next one, I would still have chosen him because he simply addressed my wishes and fears the most. That he is also in future proximity was the cream, which the third competitor shared with him as well, but he was the least committed and the most expensive... So my recommendation would be to proceed like this, because this way you don't make so much effort at first and you already filter out those who basically are into the project. Then send the proper specifications from the architect only to the interested parties or even - if many respond - only to those who triggered the best gut feeling in the first contact.