I'm fine with it being "stellar flares" in fact, it sounds even cooler, while also making more sense.

And the crash doesn't have to have caused it, that's fine. It was just a fleeting though, is all. It still could be possible one of the flares could have interfered with the shuttle craft, hence the crash. That's also possible but hey...they don't need to correlate. In terms of someone putting themselves into power, with the generations that have passed (we'd need to have a rough estimate of when the crash was and how much time has passed since then) it's likely they're not the original survivor or maybe just related to someone like that.

I do think having a very distinct line between those who have cast aside science and developed some kind of natural cult of living off the land, and those who rally behind logic and science, is the key here. I assumed most would be humans but I think it could be neat to have some kind of humanoid creature with certain differences, some alien species that's either been assumed to have been killed in the vanish of their transport craft (to say a new home planned by the Federation?) that way, their discovery would also be meaningful for historians perhaps.

Was Forbidden Planet when Geordi was stranded with that other guy who...wasn't too friendly at first? I think Geordi's vision was messed up due to the planet's environment. At any rate, I do think the other life form should be like gas or some kind of vapor/gas/mist. I would assume there would be some dust/glitter to be seen but most of it would be considered nothing or too small to detect/think about. We may also need to list some of the symptoms of what the "infection/virus" might look like to an outsider. Their resources would be very minimal, if any, even if only 30-60 years have passed. I'm sure things have waned by that point, so any new inventions, were on them and not thanks to how they crashed and what was on them at the time.

I think getting things rolling, the sooner the better, while getting down the important/main details is good. I don't want us to get too bogged down with this or that, since starting will be easy and then going over details or following one another's lead, can also work.