Big movie studios ruin everything, so I'm going to give my opinions with a smaller studio (read: more of a budget) in mind who would give the Dragonsteel crew more control.
Kel - Stephen Amell: He's 40, fit, and blonde. He played a killer with his heart in the right place in the first season of Arrow. But can he be inspiring and funny like Kel? Maybe with a better director than the CW could afford.
Vin - Amber Midthunder (from Legion). Has already played a decent badass with vulnerabilities.
TLR - I'm going to let budget slide a little here because TLR probably needs to be on set a fraction of the time of the leads. I mean I'd really like to see Bruce Campbell in this, but he's too old (obviously not chronologically) and might make the movie seem to zany (he plays a good serious role but the audience expectation might be a problem). There are similar problems with my other choices: Robert Carlysle, Gary Oldman, Javier Bardem. If we gender swapped (no reason not to, really): Michelle Forbes.
Saze - Rodrigo Santoro as Xerxes from 300 is pretty much how I picture Sazed. But I doubt that guy looks like that anymore. 300 came out when I was in college, so the dude's at least 12 years older now.