for every windows program your used to, there is an equivalent linux one for the most part, cept for games
its not all command line, there are like a dozen GUI's to choose from
perl and C++ are ok on linux, visual basic is windows only, but linux has programming languages that are very similar and quite a few more that windows does not have and never will
knoppix os ok for a live CD, as an installed distro it isnt so good, a regular one would be better
Biggest difference you will notice with linux is of course all the names for things are different, but also its based on the same ideas as unix, so anything you know about windows likely doesnt apply, but everything about unix does. Linux is much more modular and flexible than windows, and there really isnt too many limits to what you can do, no licenses to deal with either. Most things in linux can be done via commandline or GUI, and in many cases the GUI is nothing more than a graphical front end for the commandline apps.
As far as using windows apps in linux, ya you can use some of them, but quite honestly, your better off using the linux ones, they work just fine.
Im not even going to get into which distro is best LOL, pick a few and try them out, check your hardware compatibility first please, I warn all rookies about this and few heed the warning, latest to do this was john3.........I wont help if you do this. Linux IS NOT WINDOWS period, there is no other way to say it. Do not expect bleeding edge brand new hardware to work like it does in windows.