Ans 1: Already answered by @MagicSmoker.
Ans 2: Dero DAG like other chains requires block propgation time to propgate blocks. Block propgation times AVGs 99.99% ~15 seconds.
Ans 3: By client protocol.
Ans 4: 2 uncles(Dero side blocks if you are referring to them only) are allowed depending on NW.
Ans 5: RingCT is core part of Dero architecture.
Ans 6: We are still searching better algo than POW.

  Thanks for your time and questions.