You can definitely have this car maintained at an independent shop. There is no reason to take it to a dealership unless you prefer a dealership.
The manufacturer probably recommends premium gas for this car, but you will not do any harm by using regular. You may lose some performance benefit, but you will likely not be able to tell the difference.
The I30 is very similar to the Maxima. I believe that it's based on the Maxima, and it probably shares the engine with it. They will be very similar, though the Infiniti will come with all of the nice window dressings and refinement that come with an Infiniti.
The insurance is probably low. You can compare costs here: http://repairpal.com/insurance-quotes