We are considering opening an ATV park here in Portales, NM.
Can you tell me where I can find any info on insurance, track lay outs, etc?
The best place to start, in my opinion, is with the National Off-Highway Vehicle Conservation Council (NOHVCC).
This organization represents the interests of off-roaders of all kinds and the staff interfaces with land authorities at all levels.
NOHVCC has a Trail Manual that contains information about the issues you raise, although it is directed more to public land than private, this will be a good jumpstart.
Contact NOHVCC at www.nohvcc.org.