1. What are the testing metrics
The higher the confidence, the more sure one can be about the long term validity of the result. Higher confidence levels generally require more data. Hence, dependent on your testing strategy and account volume, you will decide what confidence level you'd want to first get before pausing loser ads. You can use thresholds to control the minimum confidence you want tests to first have before winners are declared.
Here is more information on what metrics to focus on during your testing:
3. Can some metrics be disabled?
You can disable metrics that don't apply to your account. Disabling a metric will result in it not showing on the test result screens, hence allowing you to focus only on what is relevant. For example, accounts that don't set a Conversion value will not have or need any test results for Conv. value/ Cost and Conv. value / Impr.
You can enable/disable the metrics as needed by clicking the Ad Testing Settings.
You can disable unnecessary ones by unselecting the checkboxes next to the irrelevant metrics.