I’m having trouble picturing what you actually want to do in the north coast areas. It’s like … there’s road. Or there isn’t. “Cycling through a farm” makes me imagine a bike perched precariously on the edge of a rice paddy, which certainly sounds like a bad idea for rider, bike, paddy, and farmer.
I certainly wouldn’t go through someone’s gate. Will that put you in physical danger here, no, but “Hey, nobody will shoot me!” isn’t the same as “Totally acceptable!” Once in a while it can be a little unclear if something is a driveway or road, and sure, there I guess it’d make sense to try it out.
For big stretches of that area, the main road IS the coast; there’s no way to get closer to the ocean unless you’re slogging your way over or around the tetrapods in the splash zone. There is a moderately lengthy cycling path from Sanzhi to Jinshan, and that’s one of the few “coastal” (as opposed to mountain) areas.
Note that dogs are definitely going to be an issue on smaller roads and alleys. I’ve never been bitten, but it’s not that unusual for me to look at several baying dogs in front me, decide “OK, they win”, and turn around and try a different route.