I'm not sure why you say that EE is a legacy system, they actually just pushed out their v2.8 a few days ago and have been updating the system for years.
If you're familiar with WordPress, the process really shouldn't be too different. You need to save templates as files and version control those along with system files. You're most likely not going to be version-controlling the database similar to the way you wouldn't be doing that with WordPress.
Simply turning to Google would probably give you hundreds of answers about how to do this but I'll leave you with what I consider to be the most definitive reading on the subject:
http://devot-ee.com/articles/item/version-control-for-expressionengine-using-git-part-1