"Back end" is typically used to refer to web development as well, so I'm not sure if I misunderstood you, or you misunderstood the term. Web has "back end" (ruby/rails) and "front end" (html/css/javascript). With a lot of the latest developments there's a lot of overlap in job descriptions.

That is really enough, yes. That's nearly "full stack." You're going to learn some sql while learning rails, and you're going to have to learn enough to deploy somewhere (I recommend heroku to start).

Basically you should teach yourself how to build essentialy any CRUD app (blogs, wikis, basic twitter, news site, hacker news, reddit, etc). When you can do that, you're employable--and probably well above average, honestly.

There will still be TONS of stuff to learn after that, but there won't be any reason for you to not get typical web-development jobs.