It's difficult to know where to begin...
Now more than ever, if you want to be a versatile dev your strongest assets are fundamentals and the ability to learn and see patterns at a high level.
There are still plenty of jobs where you can learn the current Java or .NET + C# version and have a career for life. A huge portion of major enterprise software and websites are backed by both of those techs, and they're still very viable. node.js and Python are a bit newer but the same idea, lots of jobs.
"Web dev" is a broad subject, and learning "everything" is pretty tough to do all at once. Some subsets: styling/visual design (CSS+HTML) experience design (read Don Norman), browser application programming (client-side JS), server-side application programming (Java, .NET, Django, Rails), database design, deployment and ops. If you build a non-trivial web application from scratch in any framework you'll gain experience in those areas.
Don't get focused on the "what" as much as the "how". Every MVC web framework is conceptually identical, and syntax and laguage quirks are easy to learn.
Basically, just do it and don't get hung up on the details. Or, if you have very specific jons you're interested in tailor things that way (i.e. enterprose web development -> pick Java or .NET and make some apps)