Regarding the "testbeds". I recently built this for an (iOS) application and it helps SO MUCH. Each module in the app has its own local target (the testbed) with a menu which lets you open the module for a given scenario. A scenario is a combination of local JSON for endpoints, device fakes (think fingerprint enabled/disabled) and module-specific configurations. The ability to near instantly get to a specific functionality with the same network requests makes everything super simple. I run the UI tests on these targets as well, and they are near perfectly non-flaky.

The best part is when I receive a new bug report from QA, since they include the network logs I usually just need to create a new scenario, register the JSON and fix the reproduced issue.