Thank you all for your replies. It is a massive help for me. I think I will start with unmodded SH3. I have to say I find SHIV tempting because of better graphics, but I will start with SH3 anyhow. I will install some mods (like the GWX) after getting a better sense of the game first.
And yes it is the steam version, so thanks for all the tips regarding how to install the mods.
See you in the seas