Boy, if you ever want to see all of your Thark units in one place, look up 'Thark wagon' in Google Images.
After some research, I think you can scratch the War Wagon. That came out of the "what units are available?" phase of planning, and would have been a theoretical 'thoat chariot'. Turns out that Tharkian Thoats are so large that they're like tanks anyway.
You're right about the Padwar; as I've been filling in Units on the
Master Unit List, I put the Top Sergeant #2 in the Padwar slot, and it got me screwed up. I can find another way to use the 2nd Sarge.
If you look at that Unit List you can see where the remaining units would go. I don't know what we'll do about cannon units; the Green Martians don't use them in the books (like they don't use flyers, except as passengers). Perhaps Thoat Riders with Radium Guns would do, d'ya think?
Re Hatchlings: I could only find one picture of a Thark Hatchling, but suffice to say that they're described as not too small, and able to get around quite well as soon as they hatch. 10 - 12 yrs old looking, I'd say...