Use of quirks for self-defence is legal, as we learn in the omakes of vol. 9 and 10 of the manga:
That does however not mean that being a vigilante to save other people is permitted. If you happen on an accident and have to use your quirk to save someone to prevent their injury? Cool beans. If the police end up with you doing it for the 3rd time in a week they'll investigate on charges of vigilantism.
From a legal sense the problem is pretty clear. If a civilian tries to stop a villain attack and ends up causing more damage or injuries because they messed up, they're just as cuplable as the villain. They may not have intended to do any harm, but did so anyway because they decided to take matters into their own hands. Just imagine how much damage someone like Bakugo could do if he fucked up with his quirk even once.
So, from a legal standpoint, you might be able to get away with a case of "self defence" or two, depending entirely on the situation.
So, as long as we don't go looking for villains, we just happen upon someone in danger, we are allowed to save them, as long as we focus on saving and not fighting? Because that seems like the main thing that would be happening. Our omniscience brings to our attention people needing saving, I doubt we'd be legally required to just watch them suffer and maybe die.
Edit To Avoid Double Posting:
So, I think our actions for next week should be
[] Continue working on the new miracle!
[] Dream of yourself.
[] Contact Nezu, he seems to be the leader of these Heroes, and request to converse with him when he has a moment to spare.
-[] Attempt to come to an arrangement with Nezu, learning what you are and are not legally allowed to do to save someone. For if someone is danger, it seems unlikely that you would be legally required to let them die. You are a God of Heroism, you should attempt to maintain a good relationship with Heroes and avoid the labeling of Vigilante.
-[] Offer your godly services, to help out the good fight and what not. There are many things you can do that no one else can, and you are certain that, even without doing what is traditionally called Hero Work, you can help out. Plus, any goodwill or sacrifices you earn in return for such assistance will be helpful for your followers.
--[] Mention your Sanctuary Miracle. The ability to create locations in which violence against people is impossible is bound to be useful.
--[] Inquire after the frequent medical appointments of one Toshinori Yagi. You are a Healer. If mortal healing can not help him, you might be able to. It might take a few weeks to prepare the necessary miracle, but you are sure you can cure anything short of death.
@Nitro Does Cancer, Auto-immune diseases, and other super-complicated illnesses count for Cure Disease?