Okay, to address the points raised thus far ...
PvP .. unlikely to be an issue. While characters may occasionally argue or disagree, I've only ever once seen actual PvP in a game. One of the characters had tried something dumb, ended up killing a few dozen mortals, and expressed no regret for his actions. The other 3 who were around took offense at this, the two who might have been able to talk the situation down were elsewhere, and things blew up. In general, I don't expect PvP in a Scion game.
For starting level, I'm okay with boosting that up, in conjunction with GM assigned Legend. For starting I would give Legend 3, but keep the Legend -1 rating on stuff. This should allow for more variety in characters and abilities. On that same topic, I'm okay with the concept of unofficial / fan made Pantheons and knacks, but they would require GM approval. This includes the fan made alternates for the likes of Arete and Jotunblut. Scion of Shub-Niggurath? Show me the Pantheon rules and then we'll see. I'm inclined to say no though, as I'd have my doubts about how well that would fit.
Scions in the world .. I generally favour something along the lines of The Secret War going on in the shadows of the world. Everyone knows that monsters aren't real. That shaky cam footage up on Youtube of the so called Giant? Viral ad for a movie coming out next year. The people who said they saw a dragon. It was a gas leak from the sewers, and their heads got all screwed up.
If you think about it, if the TRUE nature of the world were revealed, how would people respond? Fear, panic, social upheaval. The sort of things that the Titanspawn and their cultists would be happy to take advantage of.
Of course, if the PCs decide they want to 'go public', don't forget that there are lots nastier things out there than they are ... and they just painted big bullseyes on themselves :)
For those not too familiar with the game, you can be pretty much anything you want to. Decide what you want your character to have been before their visitation. Street thug. Cop. Archelogist. Rock star. Professional athlete. There aren't any real limits. Your divine parent will grant you some favoured abilities, but you don't have to grow into a clone of them. I can help kick ideas around, and once you have more of an idea what you want, I can help with the mechanics.