I trust your motives -- but a lot of people accuse me of being insufficiently cynical. You'd need a whole lot of people doing essentially all of their tithing and donations through the site/app before you'd be doing much more than paying for the cost of the service and maybe getting something approaching fair recompense for your time. The problem is that people are largely innumerate and don't think things through -- if they see, say, 1500 houses of worship listed (and in some counties you could cover nearly that many with a large blanket), assume an average congregation size of, say, 50-100 households, and multiply that by what they think they ought to be giving (if there weren't so many things in the way, of course), and then make the mistake of assuming that all, or at least a large fraction, of that is going through you (and that's wrong on so many levels -- the reason they see so many people in church is because those people are going to church, and are probably handing over an envelope there), then they come up with a "1%" that has little to do with reality.
As with so many things in life, it's not about merely being ethical, it's about being outwardly, obviously and unambiguously ethical -- creating a ten-storey Gothic cathedral of an ethics policy with gargoyles and grotesques and tour guides and a 24/7 information booth, then putting an enormous sign on the roof saying "This Is Our Ethics Policy", and giving people a way to check. If there's no way anyone -- not even the thickest gainsayer -- can see wrongdoing, then you won't end up on the wrong side of a plausible internet smear campaign. And that's worth as much to the congregations you're trying to help as it is to you.
