am not Marek, but let me see.
1. OpenGL 4 seems to require newer hardware. If you want to make use of certain features in these new cards eg ATI Radeon 5800 and above, then yes.
Also GLSL has been updated and also changes made to make writing shaders easier.
Best way to use OpenGL 3.0 and above it to know what you want your code to do and then check the capabilites and extensions and see if the card supports them.
You dont have to deal with them ever but once you start writing complex code, then you might need the features.
3. I'd also like the physics vmk to continue
4. For Joystick and Gamepad support, you will have to add code to your window class that handles messages for them. Read Windows Multimedia Joysticks
and check all the links in that page. You wont get support for more all the button on an xbox controller using this method but for joysticks with fewer buttons it will work. But to get any joystick to work, look at using Direct Input. (this is not cross platform though)
Music and Sound can be added easily using OpenAL (http://www.openal.org
). It uses a similar coding api to OpenGl so its easy to pick up.
Hope this helps.