>So if one were to get into The Flash, what would be a good order for the volumes? Can I just go straight through, say, Flash Comics into latter v1 and then straight into v2 post-Crisis?
Yes, although as the other user mentions, that does include Jay's Golden Age adventures. If you want to start with Barry, begin with Showcase #4, 8, 13, 14, and then pick up with Flash v1 #105.
>If I were just going to read post-Crisis pre-nu52 Flash, it's basically just v2 into Flash Rebirth into v3 into Flashpoint, right? Or are there other events/books that can be considered essential Flash reading?
You'd want to read Flash: Rogues Revenge just for a cool Rogues story, and read Flash: Rebirth #1-6 (from 2009). Plus Blackest Night: Flash #1-3.
>Jay's volume was called "All-Flash" rather than v1 and I haven't looked into why but the numbering in Barry's run starts with like #100 in v1 and also his first appearance is in Showcase. I haven't read much preCrisis to tell you more than that though.
Jay's series was primarily called Flash Comics, and it does form a good part of Flash v1. Jay's series ended with Flash #104, and Barry's series picked up about a decade later with #105. But you're right that Barry's first appearances were actually in Showcase #4, 8, 13, 14.
Jay did appear in a title called "All-Flash", but that was a different book.
>There was the Bart run I think titled "Flash: Fastest Man Alive" without a proper volume number that kind of happens in the midst of v2, like around 240 or 250, then they go back to v2 numbering after it. It's kind of shitty though. Impulse is a good ancillary book but not really required outside of maybe crossovers.
Yeah, I wouldn't recommend Flash: Fastest Man Alive.