Love to answer questions if I can.
1. The testing culture is very thorough. I was involved on the propulsion side of things, and as such the safety is taken very seriously, for the safety of the test/production engineers and of course the spacecraft. Propulsion systems are typically integrated in such a way that it is very difficult (nigh impossible at times) to separate them if an issue is found at a later stage, so the testing goes through things with a very fine comb. And even still things can go wrong and can sometimes only be found at a later stage.
From the spacecraft Assembly Integration and Test (AIT) side of things, which is where I work, things are traditional but pragmatic. If a new way can be shown to be more reliable we will adopt it. But not before it is very well understood and characterised. In space, heritage is king, the best way to know if something will work in space is to already know it works in space. So it can take a lot of evidence for a new method/system to be adopted, and when we think we are moving quickly, it probably looks like a glacial pace to others.
During the build and test, we are often so far from the end goal of a spacecraft, its not possible to see the "groundbreaking" aspect of things. Perhaps the payload designers and engineers can see this better.
2. I believe it is named after Euclid, as the father of geometry, as the mission goal was to measure the geometry of the universe. And also yes, go Europe.
3. Christ, accomplished? I love the idea of being accomplished in many ways, but its also a scary concept. Wouldn't want to be having notions of grandeur either. I am very lucky to have worked on many great projects, in many countries, and in a job that I honestly think I am good at and enjoy. But I am always surrounded by so many people who have done so much more, so it mostly feels like I am trying to catch up really.
The science missions really are special to me, I have a background in Astrophysics, and sort of fell into spacecraft engineering. So it is always a real pleasure to get to work on something I understand on a deeper level. But most of the missions I have worked on have not been so special. Most spacecraft are to make money or do something for a military. Its why I have so much time for ESA. Even with their issues (cost, time, etc.), they really feel like they do the important missions for humanity. Nasa and Jaxa too, but they mix in a higher amount of the less special stuff in my experience.
The stress and sacrifice was stressful and sacrificial(?). I wouldnt say it was worth it, or not worth it. Its an odd one. Mostly I have just tried to do cool shit as often as I can, and I have been damn lucky.
Thanks for the kind words though, and I hope I wasn't rambling too much in my response.