I have said this to many people over the past few months and don't mind saying it again. When it comes to education it depends on your motivation. Be honest with yourself and ask can i motivate myself to learn something new for about 3-4 hours a day? If the answer is no I would suggest school if it's yes don't go and learn alone.
I myself was a very unmotivated person so I choose to go to IADT toronto. Not the best school but I took a lot out of it. While there I made it my goal to be better then everyone else. I picked the top guy in the class and aimed to surpass him. Eventually I did but not until about 5th term. This gave me a lot of motivation and made me stay late study hard and figure stuff out on my own.
Before you get into the tools I would suggest you start sketching. Not great things just top down maps with thumbnails of areas of interest. In level design you have to present these 'concept sketches' to your lead to approve them before you actually do anything.
As for tools, I would suggest using hammer. (Halflife 2) as it is great for demoing stuff. Also learn 3DStudio Max. This will let you model texture and import things into your map.
You could also learn the oblivion editor. It ships with a ton of tutorials and documentation so it should be easy to pick up.
The new Unreal Tournament is supposed to come out third quarter (July-Sep) so try and learn that if you like as well.
All these editors ship with the games.
Also as far as mod groups go, don't kid yourself. A mod group is a great way to start. My friend was working on a game called 'No More Room In Hell' It's basically a zombie apocalypse mod for HL2. Before the mod is even done(still in development) he got hired at Rockstar Toronto as a junior modeler. The idea behind a mod group is to create something as a team. Get that experience and build a portfolio. Thats all. I bet you have never even heard of 'No More Room In Hell' yet my friend went to a AAA studio. That sounds like a big break to me without being a shelf title.