I can give some information on this but not everything.
Around the time of the Heian period, from year 794-1192, upper class people usually let their hair grow out and not cut it as it was seen as a sign of beauty. This goes for the guys as well from what I can tell. Anyway, since they didn't cut their hair, it would often reach past their bodies and even beyond that. The only time when it was cut was if that person were to become a nun or monk. However, monks go for the bald look, nuns go for the shorter hair look.
As for the frequency of going to temples and/or shrines, some people go often, some don't. There's a semi-tradition where, on New Years Eve, someone who had not gone to a temple or shrine all year will go to one and stay there until past midnight. This way they can say they have been to a shrine last year and this year (as well as something else but I'm blanking out at the moment).
Now this is just a theory that came to mind while writing this (so part of it is rambling), but I think the reason why they have the long hair in the movie relates to the Heian hair issue. When a person back then wanted to go into heaven (in the Buddhist religion), they would become a monk/nun, cut their hair, and "isolate" themselves from the world and follow the teachings of Buddhism. BTW, I use quotations due to example I've read in "Tales of Genji" that would take awhile to explain. If they didn't cut their hair, they weren't considered a nun/monk and weren't allowed to follow the teachings just yet and weren't guaranteed a spot in heaven (again, basing this off of "Tales of Genji" which is a pretty accurate yet fictional book). Anyway, maybe the reason they have the long hair is because they didn't have the opportunity to enter heaven and thus are left to wander the world.
Or if anything else, I think it just looks scarier with long hair.