With regards to the insurance side of things, I checked this out back in 2006 when the insurer was Perkins Slade.
We were planning on starting the NEFTA Hunter series, and we wanted to be able to have visitors from outside of NEFTA taking part in it. I think the way the insurance was worded was that any shooter who was a member of a NEFTA affiliated club was automatically insured to shoot at any NEFTA affiliated events (I don't think it actually mattered if the shoot was at a NEFTA ground or not, but I might be wrong on that).
For those shooters who were not members of NEFTA, they were insured so long as they signed in as visitors - under the insurance as it stood in 2006, there wasn't a limit on the number of visitors we could have, so long as they signed in a visitors they were covered by the insurance.
I'm assuming it's the same under the NSRA scheme - at least I hope it is because that's the assumption I'm working to for the Recoiling champs on 24th March.