5x100 48mm offset is pretty common for Impreza/WRX, so 3mm will only be a small difference. Those are pretty tiny wheels if I remember correctly though, the only Suby wheels that may be close to your size are the stock late 90s wheels, which I think are 15s. Pretty much everything else is 16 and up.
It shouldn't be that hard to match the weight, the stock (OMG they're ugly) Prius wheels aren't anything special, and 14 pounds for a 15 isn't light.

Your JDM comment doesn't make any sense, I don't think there is any JDM style for the Prius. You can't make something JDM if no one in Japan modifies them or there isn't a different model there. I'm not sure why anyone would want to mod one in the first place, they're horribly boring to drive, but that's just me opinion. I'd rather start with a Geo Metro (or a fork in the eye), they're dynamically more exciting and they actually have steering feel. That's not what Prii are made for though, people don't drive them because they're fun or performance oriented cars.