I think there should be 5. One for normal endless game, one for normal challenge game, one for deluxe endless game, one for deluxe challenge game, and one for multiplayer.
to the forums. You could combine them but you would have to combine all the freeplay files and edit the scripts for the mods, so I think it would be difficult to do unless you knew what you were doing.
We have set up a forum for the mod. Click here to visit it. All the updates will now be posted on the website, so register if you want to see the updates.
Zmodeler2 is probably the best one to use to make models for Emergency 4. All the others require you to have Zmodeler2 to be able to convert the model file into .v3o anyway.