I don't know if I'd wait @Odonata68. Some people are having problems installing store stuff as well as exchange stuff. If you have the downloaded files, it should be okay to install later. I just prefer to find out earlier, rather than later, if I'll have any problems.
@ZeeGee - I read the any game starter comments at MTS and see that the Steam version was experimental. I have discs, so I was always able to use the program on my old PC. Since I have a new PC, I haven't needed it. My computer can handle all the EPs/SPs, and store content as long as I limit the weather and spawning of all things I can turn off in options.