My plan is to do the first oil change at 4k miles (3500 now), and it's free from the dealer. Then at 10k miles I'll change to Mobil 1 and continue at the recommended 12 month or 10k miles schedule.

I remember with my Subaru WRX the recommendation was to wait until 10k miles to switch to full synthetic to insure that break-in had occurred. The theory was that full synthetic oil could extend the break-in interval due to its superior lubrication properties. I have no idea if this is true but it can't hurt to wait.

Also, about 5% of my driving in on dirt roads. Do you think that's enough to have to follow the "dusty conditions" maintenance schedule and change oil every 5k miles?