AHA - that L3/35 does look like a pretty good match for what's in those preview shots - what a cool little vehicle, I've never seen one before!
And those preview shots reveal why I was thinking of robots when I saw the tracks: I forgot there's what looks like a robot foot in the same preview shot.
I'm not sure what else i'm seeing in those previews - is that a samurai's foot? One of the torsoes looks like it's probably Napoleonic, and I suppose the other is a driver for the vehicle, as Brian suggests - or maybe I've got that backwards; the chest with the heavy harnesses might otherwise look kind of sci-fi or something???
For the model scales, I think I agree with @JTam on 1/48 scale: I've had a couple folks say 1/48 looks too big to them, but from what I've seen in side-by-side shots with 28mm infantry on bases, 1/48 looks about right to me.
I take it 1/56 is the same height as 28mm on paper, but in practice, scale creep* and sculpting proportions tend to make the characters as wide as 1/48 figures, while the bases add a little extra height to figures, compared to unbased vehicles. 1/50 is probably even more accurate, but from what I've seen of the side-by-sides, the different between 1/48 and 1/50 isn't very big.
* Regarding scale creep, a modern "28mm" is often closer to 30mm or more - up to 35mm for many "28mm" RPG minis! Some 28mm wargaming figures - especially older ones - might be closer to an "actual 28mm" (whatever that means), but it varies by manufacturer.
Tamiya and other plastic model manufacturers do make some great 1/48 scale armor, but not a lot, and I think WWII gamers are in better luck at that scale than those of us gaming in, say, WWI, Cold War, modern, or near-future settings!
I wonder if some wargames mini manufacturers might be able to kick some of the traditional scale model manufacturers in the pants, and partner up to produce some quick-and-easy armor model kits for other eras in any of these scales? (1/48 certainly seems like an industry standard for scale model kit manufacturers, and the path of least resistance for such a partnership, but I'd be happy to "settle" for 1/56, 1/50, or anything else close to 28mm scale, if that's what it takes to get the ball rolling....)
For my part, I've seen pictures of 1/48 and 1/56 Shermans next to each other, and the difference is noticeable, but more than close enough that I'd be fine with either, or a a mix of both at the same time, or (more likely) whichever is most affordable to me or at least most available/practical :D
A diesel fantasy game sounds like a blast!