
dunebugg |

TBH Divine Source really should not be a power gaming tool. You're obviously taking it because your character feels strongly that they want to be worshipped, and has certain ideals you would want your followers to uphold. It's a huge roleplaying opportunity. Which Empyreal Lord do you follow? That's probably a good start for figuring out direction you're going to go.

Xethik |

If you're already a Mystery Cultist, I agree that you should look there for ideas for domains. But, if you'd rather pick domains first, work concept later, I think that's fine.
As for domain spells, I normally associate good domains as those that grant spells clerics wouldn't normally have access to, which is the opposite for you, I feel. Getting something like Miracle from the Divine subdomain would be great and might make sense for your character, but that would require two Divine Sources. Community is surprisingly good, giving some buffs that are usable into mythic levels and some nice utility spells like Heroes' Feast. Also Miracle. You know, Community seems like a reaally good pick up, but maybe I'm overrating Miracle.
A good question is what kind of Wizard are you playing? Maybe there are some nice blasts you can pick up off the Divine list if that's you're style? Divine summoning spells (Planar Ally) for a summoning focused Wizard? Stuff like that.

aegrisomnia |
I'd recommend one of the ones that end with Miracle. I believe the Luck domain ends with that one. Something about access to any effect for no material component cost and no restrictions to speak of sounds pretty sweet. Of course, you have to wait for tier 9, but hey, why not?
EDIT: Being able to grant yourself free, unrestricted miracles is something I'd recommend only if you can handle it responsibly.
EDIT2: Just checked, and Community grants it, too.