Very nicely done. I would just elaborate that final statement to perhaps complete the explanation: Gnome 4 telling the truth does not alone make Gnome 4 clearly the tallest. However, given that Gnome 3 is the one lying, we see from their own statements that Gnome 1 is the shortest and Gnome 2 and 3 are NOT the tallest, leaving only Gnome 4 to be the tallest.

That's cute, and got a smile from me, but it's a stretch. In regular language it is clearly understood that the value of a container includes its contents, unless otherwise stated. (Is 50 cents a good price for a bag of chips? Only if it includes buying the chips inside it :)

I would guess that the details in the question which at first seemed extraneous to me must be relevant. But I learned that humans probably use base-10 because we have 10 fingers, not 9, so my guesses don't quite add up with what I know about real life. I will guess that you say they counted to 3 on their fingers (excluding thumbs), and then marked a tooth and continued until all 31 teeth and 3 fingers were marked, and then started using combinations of eyes open/shut for another factor of 8?

I enhanced my explanation a bit. It can represent all numbers, and it still even has a unique 1:1 mapping for all numbers, as long as the Martians intuitively know which digits they can use where. I'll add the details of this to my explanation. It's my first time using hidden text, so I'm still playing with it to try to hide spoilers.