I can start by saying that the new collider problem has not yet been solved and recently other things have been steeling my time.
The heightmap.raw file is the file that contains the height information. It's black and white image and black is lowest possible point and white is the highest point. .raw is a file format that not all people may not be able to edit since not all image editor softwares supports .raw editing but programs like 'l3dt', witch can be used for free for personal use, can modify .raw files in a 3d enviroment otherwise photoshop can edit .raw files. In the future when a proper map editor is made then external editors will not be neccesery but untill then making maps will be a little bit difficult.
loadscreen.png is just a image that will be shown when the map is loading and thumb.png is used for the texture that is shown in the level selection.
splatmap.png is the texture that controlls what texture is being painted on the terrain i.e. if the ground is snow, cliff, ice or whatever is avaliable in the game. This image needs to have 4 channels: red, green, blue and alpha where each channel is controlling one textrue ingame.
settings.ini is a text file that contains all settings that are available.
These are the settings that are currently available, more will be added and some may be removed later but this is kinda what the file will look like. .ini files can be editied with notepad or what ever can edit .txt files. I will not go to into depth in this file since it's not finnished but I will make some documentation when 0.3.0 finnaly launches.
How trees, rocks or other objects will be placed is not yet decided but tree placement will atleast be in 0.3.0 objects can not be promised. Maps will be available in multiplayer and you can play and join everyone as long as all of you have the maps installed. They have to be installed by sharing and placing the maps in the map folder and they will NOT be automaticly installed by joining a server, as of now.
Feel free to ask questions about map creation if you wonder anything and be prepared that things will change over time so maps you made may not be compitable with the next version but I will try to make it backwards compitable as much as possible.
sorry for all the typos I really need to go to bed.
Edit: Forgot to mention that SledSimulator has been updated to work with unity5 but I haven't upgraded the shaders yet so graphics are basicly the same