Update: I have almost all the part together that I need. The last missing piece is the gen dial, which I ordered last week. So far everything went wrong that could go wrong but I'm back on track. First off, as mentioned above, the crown turned out to be a 24-600-0, not a 24-603-0. Furthermore it is not genuine, so that's a couple of bucks down the drain. Then raffles dials send me an unbranded crown. Some other things had defects too, so he send me a second parcel with the correct branded crown. I found a 24-603-0 for 165 € online, but as the rafflesdials worked very smooth a didn't look too bad I decided to not make the build more expensive than it already is and stick with the raffles crown. Maybe I'll upgrade in the future.
The watchmaker who serviced the movement seems to have overoiled the ratchet wheels of the ETA 2836-2. Or they were defective from the start, but then he should have replaced them. Either way, the rotor spins a bit when winding the movement in a completely flat position. The watchmaker insists that this is a common ETA problem (which is not entirely false, but you can fix it) and that everything is fine. As this is not a significant problem I will be using the movement as is and have it serviced by a dude I was recommended after a year or so.
Next it turned out that the bracelets I bought did not fit the case for whatever reason and the spring bars didn't catch the holes in the lugs. I removed the rings on the inside of the endlinks, which allowed me to attach the spring bars, but now the end links had nothing holding them in place and they were rattling around loosely. Therefore I resoldered the little rings and used curved spring bars, which is a bit of a hassle but solved the problem.
This is how I want the final product to look like btw: 1998 no holes smooth bezel 36 mm Rolex Datejust 16200 silver dial
Fingers crossed that everything will go according to plan from now on. Next steps include glueing the datewheel to the movement, glueing the dial to the feet, fitting the hands, casing the whole thing and getting it waterproof.
Here are some pictures of the stuff I had delivered so far and the endlink rings I was talking about: https://imgur.com/a/0vr5E0O