I own: Core Rule Book, Bestiary, Beginner's Box.
I know about: The PRD and D20PFSRD.COM
My experience: I GM'd Deathwatch briefly, but otherwise have no GM experience. However, I have played AD&D 2e, 3e, 3.5, 4e (Don't judge me too harshly), and many other non-D&D rpgs.
My players: Five of them. One has played D&D 3.5 in the past and has played some Final Fantasy. Another has extensive experience with World of Warcraft. Yet another has played many Final Fantasy games. And finally, two of them played 1st ed D&D so long ago they don't even remember how it worked.
I list all of this to give you good sages as much info as possible that might be needed to answer the topic's question.
I know how the effective challenge level works according to the Core Rule Book. I plan on using the adventure provided withe the Beginner's Box as the first for my players. However, I do want to allow them to play any of the races AND classes from the Core book. Considering all these factors: Should I simply throw more enemies at the per encounter, and/or make the enemies tougher at each encounter? I bow to experience here