To address the last part first, your ship is small in filesize because its made of blocks. Each block already exists on every client\'s computer, fully textured and ready to go. The file, then, only has to list what blocks are at what coordinates, and with what rotation. This system is one of the big advantages to block-based building, and is one of the reasons why the same building style was used in Kingdom Hearts and Banjo-Kazooie:N&B. Notice that when you join a modded TF2 or CS:S server, there\'s a bit of waiting before you can play, due to all the models and textures being downloaded.
That being said, I had indeed forgotten that StarMade is on the Steam Greenlight. SteamWorks could certainly help out with a lot by allowing the models to be downloaded from higher speed servers rather than from each client independently. Not to mention the models used in this game are likely to be relatively small anyway, due to the lower graphics quality. The only thing the game server needs to keep track of is actual size of each player for collision calculation, which can be done by simply sending the dimentions of a box that would fully cover the model. With that in place, the only downside that players would get from not downloading a model is some clipping. So people that have slow connections could still play fine without downloading everyone else\'s models.
Additionally, when someone connects to a server, the standard model could be used until the correct one is downloaded for players that do have downloading enabled. Similar systems are used for Phantasy Star Online and All-Points Bulletin; a stand-in model exists until the actual model is ready.