Nah, it's actually a lot easier than Civ 4 it's just different because Civ 5 doesn't read data directly from XML files like 4 did. Civ 5 uses SQL database tables where Civ 4 used XML files, Civ 5 uses XML files to make SQL statements more readable, when the game loads the XML is parse to create a database table containing all of that info. For us this means we can apply changes without having to change any original files (with some exceptions). For example, I can disable all of the original civs with what? 6 lines of XML or so, or one basic SQL statement. To do the same in Civ 4 required a modified (and large) XML file.
The beauty with this setup is that my changes to the game database can exist with or without your changes to the database. I also means I can distribute a large, complicated mod in multiple pieces so you can enable what you like and not what you don't and when it comes time for updates I only have to update the parts that change, not the entire set of them. Yeah, that last bit goes against the populatiry of releaseing large compilations of small mods but it's a new concept for Civ modders so that's to be expected.
So, like Shiggs suggested earlier, start small and add a few pieces at a time. Once you do one thing that works you'll know what you have to do and it'll be easy to catch when you inevitably mess something up and break it. My first modding attempt changed the hit points of units and cities, then I added some changes to combat XP gains followed by some tweaks to the AI rules. Each step was small so it was easy for me to catch it when I messed something up (which I did, several times) and now I can add and remove things easily.
It's really a slick setup once you get comfortable with it.
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