All three are possible. The first may be contingent upon the last, although you can make it work even on a server that isn't yours, I think. I'll have to test this. Using your single player save to host multiplayer is simple, but zed spawns will reset. You copy your survival or sandbox save game folder complete into your Multiplayer folder, renaming it whatever your server is called (servertest by default). You can also copy it again into the same folder changing the name to 'IPADDRESS_Character_Name' For example, if you run the server on the same computer on which you're playing, you can connect to the server using the localhost IP address, and say your character is named John Smith, the folder would be called: 127.0.0.1_John_Smith Then you connect using the character name as the username, and all your construction, traits, and skills will be intact. I've tested this one. I think to use your character in a server you don't control you could do the same thing, but you should check with the people running the server. I don't know how it would handle construction, but perhaps traits, skills, and inventory would carry over. Like I said, this is one I haven't tested. For mods - I believe that the server and all clients would have to have them installed for them to work properly ... dependent upon the mod, of course.