I do not currently have any plans to support 3d model import, but that could change in the future. As long as the files aren't very large and can be realistically synchronized over the network for multiplayer, I don't see why not.
The game is currently single player and multiplayer with no account needed. The multiplayer is currently co-operative, but I am working on competitive modes as well that is two updates away. New update with bug fixes coming out shortly!
Thanks for your comment!