You should first decide which area to focus in. In my opinion and experience, there are really only two areas to focus in: programming or art. Art would encompass everything from modeling, texturing, concept art, and level design. Programming encompasses, well, programming... but in multiple languages. You'll seldom find a programmer in the industry who only knows one language and refuses to learn a new one.
As far as your editor question, it is best to have experience with as many editors as possible. Not only does it help you learn what's out there and what each engine can and cannot do, but it also makes you more marketable. Devs, imo, do not care if you're a "master" at one editor: if it is not something they're looking for, they will skip right over your CV. If, however, you have experience in something that you've worked with before, they'll be more likely to actually look at your resume and give you a shot. Additionally, learning level editors these days is not really hard at all... all it takes is time to learn, so if you have free time by the boatloads, learn as many editors as possible.
Some studios will require that you know other skills other than just level design. When I worked for Streamline, I was required to do a lot more than just level design. Hell, I did everything from modeling, texture work, to programming. I was a special case, though, I think, since I have a good programming background as well. Anywho, it all depends on the developer you are applying to. While it definately would not hurt you by learning how to model and texture, some studios may not require it for a level design position. It will, however, make you that much more marketable.
As far as leading LDs in the industry... it's not gonna happen. Lead positions in ANY developer studio requires industry experience, not mod experience. While you are leading a mod, yes, it does not demonstrate your leadership ability within the actual industry. You may, however, be able to negotiate some sort of senior position, depending on how they gauge your leadership abilities, but even that is pretty rare, imo.
Overall, I think you just have to decide where you want to go, and learn everything you can about that field. If you want to be a leve designer, definately learn as many editors as possible, especially Unreal Editor. Learning secondary skills, such as modeling and texturing are a big bonus as well, so start learning!
