ok im gonna do family crest once i get lvl 59 magic.. it says the guy is in lvl 5 wildy... can i be attacked while fighting him?

The Wilderness is the Wilderness so yes you can. But I've never heard of anyone being attacked while on that part of the quest, you can always tele if you feel threatened or are being attacked by a player.

and also my friend todl me that i only need to cast those 4 spells to beat the guy.. is that true???

In order to be able to kill the demon, you have to hit (that means actually do damage to) him with each of the four blast spells. Then you can kill him with whatever method you want (range, melee, furhter mage), but he won't die immediately.