Working from #4 on your reply backwards.
The stackup? You posted it:
Here is the detail of the reference design layers:
4 signal layers (ML4, ML5, ML6, Bottom) is not consistent with good signal integrity and power integrity practice. 11 layer boards are not standard. Check with your fabricator and / or hire a specialist.
#3) The tricks are complex to write out in one sentence to a newbie on a forum. I'd suggest practicing with the tool for a while and ask specific questions.
#2) No. Router Performance is an option. Perf. L gets you constraints.
#1) 6 signal layers is 6 signal layers. Power planes don't count no matter how hard you try.