My biggest concern is graphics. I have absolutely no concept of graphics and am not exactly an artistic guy. What do you do for graphics?
First, which platform you want to program for? If you know C# and Java. You can choose from Android, Windows Phone, PC, Linux and Xbox 360 (although I heard that Microsoft no longer support XNA framework). You didn't specify on which platform you want to develop, so I will assume that you will be developing for PC.
Second, you will need to choose your graphics library.
Here are some choices: SFML, SDL, OpenGL, Allegro.
Ok, so SFML, SDL and Allegro use 2D graphics, but not JUST graphics. They also give you tools for sounds, input, network.
Pluses of these libraries is that they are easy to learn. SFML is probably easiest to learn, is fastest, and has real-time scaling and rotating, while other 2 don't. Also, SFML is based on OO Design, while others aren't. SDL and Allegro is kind of outdated. But with SDL you can make games not just for PC, it's cross-platform.
My recommendation would be SFML. It has bindings to C# and Java.
And now comes OpenGL it's a hardcore graphics ONLY library. You can do 2D, and 3D graphics. For 2D graphics you should know basic trigonometry. But 3D is little bit more involved. So if you will go with OpenGL I recommend you to start small, and don't just dive in 3D right away.
OpenGL is supported by both C# and Java.
Oh I forgot to mention that you can use SFML + OpenGL. So that you will use OpenGL for graphics, and SFML for sounds, input, etc. That's a really great way to go.
Of C# and Java, which would be best? (I know, I know.. the generic no language is best answer). What's positive/not-so positive about each of these languages in game development terms?
I myself use Java for android game development. I had no problems with it. I have never used C# so I don't have opinion on it.
Ok, we have programming part sorted out.
am not exactly an artistic guy
Me neither, but you can always find free sprites and graphics on the internet for starters, and later on you could hire someone to do the graphics for you.
For more in depth game development I recommend watching Extra Credits on youtube.
There's alot more, I recommend subscribing him, he uploads great videos every week.
I hope this post helped you at least a bit. By the way, sorry for my imperfections in English, and for stupid grammar mistakes.