Its hard to get started in EM5 modding if you are not german because most guides are in german and the most active modders aswell (see Wuppertal and Bieberfelde).
About your question
EM20 includes EM2017,EM2016 and EM5. Where EM5 is the base game and the other three "DLCs" mostly add new Singleplayer Campaign stuff and like two new vehicles.
Note: These "games" comes all with the same editor and have the same endless and challenge mode. So if you would use EM5 to build a map you can still play it with EM5 and vice versa