Welcome to the forums, have a fishy stick!

It's going to be an excellent adventure if you have some patience and some reading ability

First and foremost, do yourself a favor and read this website: http://tesivpositive.animolious.com/?page=intro_to_mods.
From that site, Learn how to download mods, file formats etc. before you decide to jump into complex mods (yes, FCOM is one of the more complex ones). Read other sections and step by step procedures as well.
My suggestion is to learn Wrye Bash's installed BAIN also (rather than getting Oblivion Mod Manager, try Wrye Bash instead), as it will save a million headaches when you try to troubleshoot crashes that are guaranteed if you don't read the instructions and follow best practices.
PS: If you have no idea what the last paragraph means, that's fine. Read the website, it will explain all.
PPS: Modding the Steam version is possible. AFAIK, it requires some tweaking of OBSE, and some conflict with a 4GB patch if you can use it (you need Win 7 64 bit for that), but that's about it.