Tbh it all depends on if Hagoromo was born after the War or before.
If he was born before it is likely he was the first she shared the chakra with.
If he was born afterwards he was definitely not the first because Kaguya was said to have had used the chakra she gained form shinju to stop the war. (making it most likely that she gave the chakra to all her men (knights and stuff not men >.>)
It's still to be explained. We don't really know how Kaguya actually stopped the war. All we know is that Hagoromo was the first to be born with chakra. Apparently, only through bloodline was the chakra shared, or at least to Hagoromo. What I do think is that it was Hagoromo who shared chakra in some way to all people, rather than Kaguya, whole I believe used it to forcefully stop people from fighting. Whether he was born before or after the war it's not relevant I think.
Oh, and don't take religion for benefits. Religion isn't about getting something material wise, but spiritual wise. I'm not going to get deep into this, but I believe you should consider heading towards a religion.
