The Flynn thing is (mainly) about his contacts with Russia after the election. The investigation about contacts during the campaign, to the extent anything is known about it, focuses on other people like Manafort (however much Trump likes to pretend he never had anything to do with him).
As Jen points out, no, we don't know much - but a lot of people and instances who know more have judged that there is enough evidence to have serious investigations. I'm sure you noticed that a number of Republican senators felt the same way about the timing of Comey's firing as the rest of us did.
As for crazy conspiracy theory nutjobs - I'm sure you've also heard that one of the reasons being cited for the Comey firing was the crazy-conspiracy-theory-nutjob-in-chief's resentment about Comey having denied his idiotic wiretapping claims.