Regarding Thawne, I'm all for the Rogues being the villains for a first film, but I do think Thawne should be seen, maybe toward the end, just observing Barry from the shadows or something? We'd see him, Barry wouldn't. If they kept the character in the shadows (minus the glowing red eyes?) they'd not necessarily need to cast him ahead of time either.
Maybe then leave him out of, or repeat the same process for a second film, and then have him the villain in the third (and possibly final? film). I'd use Grodd or DeVoe as the villain for the third film, or maybe a combination of the two.
The Rogues should probably consist of a minimal line-up, specifically;
- Captain Cold
- Golden Glider
- Heatwave
- Weather Wizard
- Mirror Master
I don't think we need to worry about Mick Rory on Legends; that character is no longer the standard villain that he initially portrayed - I guess the CW made the most of a creative licence; he's very much an antihero as far as Legends are concerned, maybe even a hero to some degree.