First test with the water washable resin was a success. I did not react badly to it. Maybe the issue previously was not just the resin, but the fact that I had to clean it in isopropyl alcohol. But this time it went smoothly.
I'll do another test tomorrow to see how that one goes.
One thing I learned though was that the supports I added could perhaps be a little thinner and the points of connection to the model a little smaller, as the supports were a pain to remove, with bits flying all over the place when snapping them off with the cutters and having to use a lot of force to break them off, which tired me out enormously. However, the part itself was really sturdy, did not bend or crack or have any issues, even from that rough handling. Will do drop tests to see how it fares. But it seems as hard and durable as the casting resin I have worked with before.