Originally Posted by Volk Z

1st question with answer- Intakes alone will not throw your air fuel ratio off enough for your engine to blow. Forced induction is really the big one if you put on an N/A motor that needs a tune.
A tune is a good idea though to optimize the performance the intake offers but not necessary.

2nd question with answer- Amsoil is the "best" motor oil. It was the first in synthetic oil for motor vehicles after synthetic was used in aviation.
That being said all cars like different oils better then others BUT I ran amsoil high performance motor oil in my 350z which is basically the same engine and the car loved it! Better gas mileage and clearly better performance.

If you don't believe me about amsoil google Amsoil vs. Mobil 1 or any other motor oil that 3rd parties did and the viscosity break down and other key aspects of motor oil blew away the competition.
Another good one is Redline or Royal purple.

Hope that helps.