FWIW, I make my living selling you (or trying to sell you!)
GURPS stuff . . . and I'm with the people recommending that you go with "gods just
do stuff, no need to justify how to the players." The moment you stick a rules system on what gods, even minor ones, can do, these things happen:
- You change your story to suit the rules. That means you're no longer telling the story that you planned to tell. No matter how "open-ended" your chosen system ends up being, it's the work of someone who isn't you, and will have biases, tells, quirks, and foibles. That means it will do things a certain way ("within the range of what these tables allow," "within the constraints of the powers system," "within the limits of this author's imagination," etc.), and that might not be your way.
- You make it possible to "game" the divine. Thanks to the system's inevitable "fingerprint" (see above), the players will eventually deduce which rules you're using and realize that the gods have to operate within their limits, however generous. Then a certain kind of player will try to abuse that system, if only to escape divine retribution or make their gods-given powers more powerful for the points.
- You paint a target on the gods. Gods with point totals, or at least parameters, fuel an arms race as a certain kind of player goes beyond simply trying to "game" the divine and actively seeks to have their PC ascend to godhood, outdo a god, or even kill a god. That suits far fewer types of stories and campaigns than it doesn't suit.
As the GM, you're the campaign's ultimate god in some sense, and you should be able to do what you want without having to explain how or why. Yes, of course you owe your players common courtesy, even-handedness in your take on the rules, and the campaign they signed up for. You shouldn't throw your weight around in those regards. But neither should you be bullied by players into explaining what gods do – how high a level, how many dice, how good a roll, etc. You don't owe that to anybody!