What is the 1Hz for?
If you use 485 for the remaining wires you only get one signal, if the 1Hz is needed then that's it. If not you can implement another signal.
Such a signal can be used to say differentiate between an address byte and all others, this takes the load off the slaves as they only have to look at the line when this signal goes low. They read the following address then if it's not there's they can ignore the line until the next time.
If you have spare wires it's not a bad way to go.
As to whether 485 is required for this, probably not although I'd use it, especially if the line is long and/or subject to noise I can't find if you said how long).
We normally avoid the east coast, too many people, but at the moment it's the fastest way north where (hopefully) we can get warm. That said we pulled into a rest area 5 days ago and are still here so I guess we can't be in too big a hurry.
it was further than we thought!
Probably about the same as the length of the UK.
Rob