Answer to all three is no.
The school is cooperative, but that's because it's a small school district. There is actually no formal GATE program and nothing additional to access - i.e. he doesn't need some WISC-V score to qualify for some program. There simply isn't any additional program. Every student identified as gifted gets an IEP. But they are very accommodative - for example the IEP in math so far is to have him teach other kids (learning through teaching the material and further develop social skills), and giving him time to do epgy on his own. In the future that can be working on AoPS homework or whatever.
We don't have to know and won't second guess ourselves. I think just watching him over the past few months have us pretty convinced.
The reason why we are thinking about individual testing is because 1) he seemed to be hitting the testing ceiling on assessments that he had done so far; and 2) individual testing seem to evaluate more areas and possibly come up with a better plan for the individual.
It is precisely because of the cooperative school that we are thinking about individual IQ testing. If there is a structured GATE program and some kind of track to follow, we'd feel better. But now the school just came back and said okay your kid is gifted, here are some general guidelines in what we plan to do, what do you want to do within these general guidelines? We don't know how to come up with an education plan, but since we are offered the chance to help shape it, maybe individual IQ testing will provide additional information. Or if he qualify for DYS, then there's a possible resource to help shape the IEP.