1. Which of the goals defined for our service is most important to you personally?

This is subjective, and as such, there is no right answer. Personally, it would have to be readability or testability. If the code is easy to read, then I can figure it out easier and probably remember more about it as well. On the other hand, if it's more testable, then I can leverage that fact to write more tests. With more tests in place, I won't have to remember as much and can let the tests make sure everything performs as I need it.

2. Which of the issues outlined seems to be most urgent or important?

This is also subjective. It might surprise you, but I would say lack of isolation in tests. With the tests as they are, every test is somewhat akin to an end-to-end test. This means that the test setup is lengthy and when something goes wrong, it will be time-consuming to figure out where the problem is.