He's right, there isn't actually any standard pronunciation of Norwegian (But for some reason we have two standard written forms). Since it is built up on dialects, you don't have to use consonant mutation, because some dialects don't. However, the dialect known as East Norwegian (which accompasses several different dialects and sociolect) is generally seen as what could be considered standard Norwegian, and that dialect uses consonant mutation so I would advise you to learn it.
Norwegian has a pitch accent system, yes. https://en.wikipedia.org/wiki/Norwegian_phonology#Accent & https://en.wikipedia.org/wiki/Pitch_accent#Norwegian_and_Swedish