Eagle I have not been lately but can give you info based on riding there 5 years ago!
You will be just fine riding on razrs! Sometimes its more fun because you can whip it around easier
When I used to go they were not really THAT careful with checking DB's. If you roll up at 75% throttle and its loud, they would check you. If you rode up at lowest throttle possible you would be ok as long as you have sparkys (which you said you do). I used to ride with a sparky in my MBRP pipe on my DS650 and it was 106DB but they never checked me so I was ok.
Your 10FT flags are A-OK. They used to sell flags at the parts shop on the dunes parking lot too so if you break one or cant get some in time you can buy them there.
If you have never ridden dunes before I must warn you: its a blast and you will be back