I'd say the pool generally works well. Of course it's impossible to create a perfectly accurate admissions system, but I've never seen any evidence that the college you apply to makes any difference to your chances of being accepted. I know plenty of people who were pooled at some stage (some of them twice!), so the pool definitely has an impact.
I don't know anything about scholarships for German students, but in my experience scholarships for anyone at an undergraduate level are rare. As an EU student you'll be eligible for the same financial support as English students, inclusing the cambridge bursary if your family's household income is less than £42,620. According to the admissions website
"The Universities Minister for England announced on 28 May 2019 that students from the European Union starting courses in England in the 2020/21 academic year will continue to be eligible for home fee status. This allows the University of Cambridge to confirm that the fee for undergraduate EU students who are already studying at Cambridge, or who will start their studies in 2019 or 2020, will be at the applicable Home rate for the duration of their course. They will also be able to access financial support for the duration of their course."