I'm planning to program simple taskbar manager for Linux like Tint2 but with my own ideas implemented. It'll be some kind of mix between unity and tint.
I have experience in OpenGL, C++, Python...
You should have an understanding of how X and window managers work. You may want to learn about startup notification as well.
This is too open-ended to answer.
... Eleventy-seven?
No. But you should understand ICCCM and EWMH so you can play nice with them.