Make sure your drivers are fully updated. Are you on Warcraft 1.31? What is the output of the console window (the black window with text)? Refer to
this document.
Loads of things, but first being able to make maps fully in HiveWE. So things like an object editor, better doodad palette, unit palette, region palette. You name them.
Improved selections is coming at some point. Maybe not per se in 0.6.
I haven't tested on Windows 7, but it should work. Check that your computer supports OpenGL 4.5, that you are running Warcraft 1.31 and what does the console window say? Refer to
this document.