So… in my mind, the "correct" skill level for this competition would be wherever you're currently at. You would just pick a different game or a different twist on the theme or whatever, to suit you skill set. And I think it is not completely unreasonable to think that somebody with absolutely no programming experience at all (I know you're somewhere beyond that) could use my tutorials or something like that and have a game within a month. It may be Tic-Tac-Toe or Pong. That's OK.
The way I'm envisioning this competition, it's not really about beating everyone else, but rather, it's more like, after 30 days, if you have a functional game, you win. If you don't, you lose. Everybody would pick the scope of the game they choose to make based on what they think they can realistically create in the time limit, with their current knowledge, and with the free time that they have available for the month.
If we had lots of people, I could imagine dividing things into categories and picking user-voted winners for things like "Best Game Made by One Person", or "Best Game Made by a Complete Noob", or "Most Creative Idea", or "Coolest Special Effect", etc., but if I had to guess, I'd say we probably won't have enough people joining to make this meaningful right now.
So to answer your question (er… uh… your self-reflective statement…) I think you said that you've been through the C# tutorials, more or less, and recently so. That's perfect. I'd say you should have at least gone through the C# tutorials up to and including the ones about making your own classes. It's going to be hard to program without at least that much C# experience.
Then I'd say start going through the other XNA tutorials (this assumes that you'll be attempting to make your game in XNA). Get XNA set up in Visual Studio 2013 Express for Windows Desktop (or in Pro or whatever, if you've got a different version, but VS 2013 Express for WD is the latest and greatest).
Then go through the introductory tutorials and on to the 2D tutorials. You don't necessarily need the 3D tutorials. It's quite possible to make your game for the challenge in just 2D. Indeed, the 3D world can be a much trickier place, because it requires some basic knowledge of matrix math, matrix transformations, and more about how graphics get drawn on the screen. My tutorials (hopefully) do a good job explaining this to you, but there's little doubt in my mind that a 3D game will be significantly more complicated than a 2D version.
You will also want to go through the audio tutorials and the input tutorials, assuming your game will have audio and input from the user. Keyboard and mouse input is easy enough. If you've got a wired/USB Xbox 360 game pad, you could go that route as well. (They work just fine on a PC. Windows is smart enough to find the drivers for it.) But there's no doubt you'll have keyboard and mouse input.
Sound is usually pretty straightforward. My tutorials get into using XACT, which is I suppose the "preferred" option, but it's far easier to use some of the simple mechanisms they added in XNA 3 (I think?) to play music and sound effects directly.
The thing about both input and sound is that you can probably ignore those tutorials at the beginning, and when you want to add those in, go read the tutorials as needed.
Two areas that I wish my tutorials covered better, but as of yet fall a little short is on putting all of the pieces together (that's what my game-from-scratch tutorials would be for) and in detailing some of the math that could be useful (or required, depending on the game you choose to make). I'm in the process of writing a book for game math, but that's nowhere close to being done. So when you run into trouble in these areas, the solution would be to see if Google has an answer readily available, and if not, post in the forum and see what others here have to say. I don't answer every question (I wish I could, but my time is limited, and if a question comes in at the wrong time, I can't answer it) but PiscesMike and Embliss have done a good job jumping in too. And if you don't get a response, keep playing around with it and after a day or two, report back on what you're tried and tell us if we're still stuck. Sometimes, just having a second attempt a few days later gets you better luck.
The best way to tell what tutorials you still need to read, or what information you still need to learn is by trying to make a game and seeing where you get stuck.
Sorry for the long response, Swatacular. I have a tendency to post long rambling answers sometimes…