My forte is high detail hard surface modeling. I know basically the entire Polygon and Mesh set of menu's and anything that corresponds to that set of skills( at least i do my best to, I'm sure there are some things that i have yet to discover even after this long with 3d work).
But i learned recently, that i have in some ways shot myself in the foot when it comes to presenting myself as a professional. While i am Very good at what i do. I have as well paid too much attention to one specific area.
The best advice i can give you as a freelance Graphic artist, is to yes, Pick one field you want to know through and through, be it modeling, Animation, Rendering lighting and Shading, Rigging dynamic SFX, ect. Make that choose. Then as well learn a good general overview of the rest also. At least , at the very least develop a descent understanding of Rendering, Lighting, Shading and riging with what every you do choose.

The age of hte Tutorials on Simply maya actually do not hinder you to much. you just need to know the language of the UI as its changed over the years.
What was previously called Polygon in the Polygons Menu set, is now referred to as "Mesh"...like wish what was previously referred to as Nurbs in the menu system, is now referred to as "Surfaces".. unfortunately this isn't a solid change in Maya, meaning its not a complete translation I.E. the Split polygon tool was not changed in name to the "Split Mesh " tool. But after a few hours using the program you'll be able to 'translate' this in your head no problem. Just remember if you hear Nurbs look for Nurbs and or Surfaces, and if you head Polygons look for Polygons and Mesh both ...
a few new tools have been added to modeling, since older versions, Split edge loop tool, offset edge loop tool, some like that, so you wont see them in older tutorials since they are newer functionality. There are also several different methods to achieve the same goal in Maya, you'll just have to experiment over time with which one works best for you. Sadly at this time i cannot tell you of the changes to other aspects of Maya as i am not well enough acquainted with them in older versions to speak to their changes through the years.

The help system in Maya is very intuitive as well, it will tell you everything about any tool, Google is good for this too, you can Google instructions for something you want to learn how to do if you cannot find a video tutorial here to show you.

probably the most important advice i can give you though is Not to give up, and Not feel overwhelmed. Break it into parts. if nothing else, Pick a tool, or two or three tools a day, Create some form of primitive object, and use the tool to see what effects you can have on the primitive with those tools. after a while you're start to get a feel for the program as a whole. Don't get discouraged, I've en working for ten years, with this program and i learn something new at least once a week still. Post your work on here in these forums WE will look at it, and give you our advice and share our knowledge, You've picked the best place to start learning That i assure you. The community here is the nicest and most helpful on the internet.
That being said, I look forward to seeing your work once you start posting. and if you need help feel free to ask any of us.

Welcome to Simply Maya
G-man