The size of your land-ship is based on one thing: the thickness and strength of the ice. That's the consideration made in situations where the weather gets cold and people want to take vehicles on the ice, either for recreation or for business. For an introduction to that topic (which is a side discussion of your basic question), see http://lakeice.squarespace.com/bearing-strength/.
Now, as for the vehicles, you DO NOT want your people living in the vehicles. Commuting is fine, but a traveling community cannot be as economically productive as a stationary community. We've seen this with every culture that has gone from a migratory lifestyle to a sedentary lifestyle, such as the Mongols, any number of First Nations in the Americas, and (to a lesser extent) the Roma in Europe and the Americas. Yes, I know it CAN be done, in theory, but that doesn't mean that it SHOULD be done. Having a sedentary population will make it much easier for the populace to support itself economically, and that's going to be VERY important on an ice world.
Additionally, if you did have a migratory populace, they need smaller, single-family vehicles, rather than massive population vehicles that house the entire populace. Frankly, people fight, have social conflicts, get kicked out of the community, start feuds ... any number of social problems that are usually solved by people separating from one group and joining a different one. So instead of massive traveling cities, you would have a convoy of ice-vardos. (see https://en.wikipedia.org/wiki/Vardo_(Romani_wagon))
OK, with all that being said, there are several questions that will shape your vehicle design.
- Do your vehicles travel on fixed routes? If so, you need some form of track or road-bed. Tracks are better for low-frequency, high-weight traffic (like trains), roads are better for high-frequency, low-weight traffic (like cars and trucks). In this case, the vehicles will be designed to travel on the fix route.
- Do your vehicles travel over smooth ice? For the most part, unless you are positing a very cold world with little or no atmosphere (like an Earth-sized Pluto), you might look at sleds or skids for your non-motive support, and wheels or tracks for motive support.
- Do your vehicles have to deal with inclement weather, over and above the cold? In this case, higher-traction and more powerful motors will be needed.
- Does your planet have a survivable atmosphere? If not, you're going to have to look at the precautions and safety equipment the vehicles will need. Antarctica and Pluto may look similar on the surface, but the need for pressurized cabins will make for significant engineering challenges.
With those questions answered, I might be able to whip up my concept of a terrific ice vehicle--but my concept will not be your concept. So think about the questions I've asked. Think about questions I've not asked--because I haven't even begun to cover the possibilities. See what you can come up with--or if anything above is not clear, leave a comment and I'll do my best to clarify.