There is state pre-emption so the county cannot establish their own restrictions.
You can carry your dual- setup on your own property or anywhere else not prohibited- there is no restriction on OC to that end. You cannot conceal more than one gun, but that's another issue.
According to NMSA 30-7-4 (4) (negligent use of a deadly weapon, consists of): "discharging a firearm within one hundred fifty yards of a dwelling or building, not including abandoned or vacated buildings on public lands during hunting seasons, without the permission of the owner or lessees thereof." - the distances you indicate should leave you being ok. Just be prepared to deal with people wondering what's going on and possibly calling the authorities. Be sure to have a proper backstop of course.
For future reference, handgunlaw.us has the essentials and also use the NM Compilation Commission's new website for perusing the statutes and rules: