Hecate was self-explanatory, as she was the Greek Goddess of Magic and thus the perfect option, her nature was almost perfectly aligned with his, but it was there where the problem lied.
Given all his actions and abilities, it was possible that she would smite him down on the spot due to his potential to eventually claim her domain of magic and thus divide he authority in that domain, though that was probably his paranoia talking, after all there were plenty of other Gods of the Magic Domain in other pantheons.
Circe was second given that she was practically the most powerful sorceress found in the Greek Myths, though this came upon the slight snag that she was giant man hating bitch that would probably kill him just for the sake of it.
Still her powers as described in the books would only be comparable to his current ones and thus much safer to contact that any of the other Gods, she was an immortal being that was described as both mortal and divine in the myths and thus she would be the perfect one to ask for the ritual in question.
And thirdly was Odin, his nature as a God of Magic and Wisdom matched Nicks domains well and as he was the God King of the Norse Pantheon his knowledge of Magic was unparalleled, he was also shown to be quite good natured in the Magnus Chase books.
But there was one big downside, he wasn't a Greek God so Nicks allegiances would be immediately called into question, after all who would arm their enemies? That would also hold the other way as Zeus and the other Gods might doubt that he was a spy sent to destroy them, given their simply incredible paranoia.
On the other side of that was that if the Greek Gods really wanted to keep this knowledge hidden and out of their children's hands Odin might just teach it to him to create problems for them.
He spent the next few days training and deliberating and doing even more in depth research before he finally settled on one choice.
After much thinking Nick finally landed on Circe. After all his safety was the foremost priority and both Hecate and Odin were Gods that were way outside his capability and thus by asking them to teach him would put him at great personal risk.
Circe, however, had no such restrictions, after all, he could probably hold his own against her if it came down to a fight. But to do so he first had to get himself in top personal shape, after all his physical abilities left much to be desired even with the magic blessing him.
And as the Greeks viewed that it was the mind, body and soul that constituted a being, he figured that it was obviously quite important to get his body at least close to the same level as his now expanded mind and soul
~3 years later~
In the past three years Nicholas completed a few more objectives. Firstly, he completed the 3 left over Rituals to boost his father's affinity for the Elements, unsurprisingly the results were nowhere near as impressive as Nicks but the still were quite satisfactory.
Jonathan could now use intent casting for the Elemental spells, though their power was minimal at best, being barely able to create enough water to fill a glass or enough fire to light a wooden stick. He also managed to awaken his 6th sense, allowing him to keep track of the entire mansion 30 meters in diameter.
Apart from that Nick also had to create a spell that would cloak a room in a small confusion charm for an extended period of time, as to hide the now 8 continuously running Rituals in the study. He didn't want any possible leaks of the source of his power.
The spell was made so that any mortal who entered the room would subconsciously think everything within it was normal and would then immediately forget what happened as soon as they left the room.
The effect was so mild that he was able to make the spell last 30 years upon only one cast with his boosted authority.
He also verified that any Rituals he now did using mortal offering would be essentially useless and not grant any boost whatsoever to the Elemental spells and a negligible boost to any other Spells, of approximately 20%.
The rest of his time was spent in an insane loop consisting of, cast a spell to block out pain and fatigue, practice until your ligaments and muscles literally tore from the stress, heal yourself using the Healing spell, rinse and repeat.
Though the process might sound ghastly in effect it was actually quite boring due to the pain and fatigue blocking spells. The results were still quite astounding, with the healing he was still in tip top health but his muscles at 11 years old looked quite remarkable.
He could, without any spell enhancements, now comfortably carry 200 kilograms without breaking a sweat, and his speed was close to 20 meters a second. With the spell boost that made him on par with the Hulk if only for 3-minute bursts at a time.
He also finally went out to hunt some monsters, the reason that was necessary being that even if Rituals that enhance him permanently were out of the question, he could still use the monster loot to cast temporary boost spells.
Hunting the monsters with the lowest "interference" to his prescience was barely an issue just an Earth Spike made with a Common Spell could kill them from a 300 meters away with them barely being able so sense him.
So he spent 2 hours every day casting the wind speed spell that would carry him all over the city and forests surrounding it hunting the monsters that to his prescience seemed to have the lowest interference level.
Through this he managed to come upon a peculiar discovery, the monsters didn't chase his scent anymore. In the past he would have to actively be running away in advance using his prescience to stop them from finding him, but now, they no longer did so.
In fact, the monsters with the lowest interference such as Empusa, Harpies, Lamia, Imps, Boggarts etc. would now actively run from him as soon as they caught his scent. While the bigger monsters would no longer chase him and would leave him alone.
Using these facts, he managed to conclude that his Rituals were in fact also boosting his smell to the monsters and Nick guessed that now that he was comparable to a Minor God in terms of combat ability they left him alone, if only for their own self-preservation.
After he collected enough monster loot, dropped after vanishing into golden mist, he finally had enough to start experimenting for at least the first dozen Rituals.