1. According to Sayyid Sistani all of the required washes, whether 2, 3 or 7, are mutanajjis (assuming it is being done with little water), irrespective of color.
2. Yes, as long as you have washed off the najasah
3. If the tap water is connected to a source that is Kurr then yes.
3. Yes, if you are kathir al-shak, someone who doubts a lot