Based on what I've read, he isn't. If no conviction is necessary, the Colorado judges laid-out the evidence in their decision. Should be case-closed. He clearly encouraged it, gave "aid and comfort"...so he's not qualified.

They made their argument. I don't think it's a "case-closed" argument. The events of January 6th were so different from the Civil War insurrection, and Trump's "engagement" with it was so different from most Civil War-era politicians' participation, that there's a ton of room for SCOTUS to conclude that those terms don't embrace the 1/6 scenario. Or that the specific language of the 14A doesn't embrace the Presidency. Or that that the CO Court erred when it applied Brandenburg v. Ohio (the case that governs when speech moves into unprotected action). Etc.

There's at least a half-dozen tough determinations on which SCOTUS can base a decision overturning the case, if they disagree.

As for your standing question, not every disagreement about what the law says constitutes a "case" that the U.S. judiciary can adjudicate. To get into court, you have to be presenting to them a dispute between two parties over something that the parties have a specific interest in that is distinguishable from general public policy, such that they specifically have an injury if the law isn't applied properly. There's lots of case law that says that people don't have that kind of specific individualized interest in "who the President is" (or who the governor or mayor or whomever is). That's why Orly Taitz had all of her cases thrown out.

"Indeed, the Supreme Court has "consistently held that a plaintiff raising only a generally available grievance about government — claiming only harm to his and every citizen's interest in proper application of the Constitution and laws, and seeking relief that no more directly and tangibly benefits him than it does the public at large — does not state an Article III case or controversy."

casetext.com - Taitz v obama

So the only folks who have standing after the election has happened are those who have the power to bring actions on behalf of the public rather than themselves. Congress has the power to impeach. The Attorney General probably has the right to file a writ of quo warranto. Before the election, candidates and campaigns have standing in contesting candidate qualification under a lot of state statutes (not federal ones, because the states determine those issues). Afterwards, not so much.