Definitely do what feels right for you, and don't lean too heavily on lore--especially for the things that aren't specified.
When I think of using magic, I think of it this way:
You need intelligence and willpower to be a successful mage, because it takes power of the mind to make magic happen. You have to summon the magical energy from its source, which exists deep within you, and you draw it out like water from a fountain, letting it flow through you and directing it to your fingertips to make it do whatever it is you are trying to do. It takes great concentration to focus the energy into power, thus creating the spell.
Spells also rely on certain words and chants. Many mages, especially those who are still learning, need to speak the magical words aloud (don't try to find the magic words in lore, because as far as I know they don't exist), and that's how spell tomes and scrolls come into play. But the more learned mage can speak the words in his or her mind, only speaking them aloud when they need the added concentration of talking rather than thinking.
Anyway, that's generally how I look at magic. But again, it's your story--your creation. Go with what feels best for you.