Basically, Humanoid allows you to use and gain bonus with equipment equal to its level. So, using a Weapon gives you an attack bonus, not a boost bonus. Weapons do not combine with other attack skills.
Magic attacks main benefit is gaining bonuses from the Magic Boost skill.
Dice gained from any single skill, if not stated elsewhere, is 1 dice, but if its level is 5 or more higher than a comparison skill (attack skill higher than defense skill, for example) it awards two dice instead.
I hope this helps! Also, download the quick start guide for more tips!