You only need the latest beta patch, 1.07.831 or whatever. You just extract it into your /Steam/Steamapps/common/IL-2 Sturmovik Cliffs of Dover folder.
After that though, I'd clear out the cache folder in your /Documents/1C Softclub/IL-2 Sturmovik Cliffs of Dover folder. Just delete the whole cache folder in there, the game will repair it when you start up the first time.