The report post is the little yellow triangle at the bottom of the post. Report it and tell them you put it in the wrong section.
As far as the insurance, I have the normal free ($1500 IIRC) insurance and wasn't asked any questions. I just had to fill out the request for it. If you are looking for more than the standard amount then they might have a couple, not sure. I'm sure someone here has the extra and can help more.
I get the free insurance also and my wife gets it too so basically double the insurance. No questions asked about serial numbers or anything like that. They do ask if you have more than that value trying to get you to upgrade the amount for a fee of course. But even the extra charge for additional insurance seems reasonable
No SNs or photos needed. Guns over a certain value, including accessories like scopes, need a description and value estimate to be compensate full value. The ins coverage is in addition to any other ins you have, so for example if you have $2k through homeowners ins and claim $5k through the NRA ins, they would pay out $3k.