Trying to make software for Instrument Control

Hi, 

I am a beginner to instrument control using VISA. I have used the R&S Forum application to control instruments in the past over VISA (USB/GPIB). But now I want to make a proper GUI. And I have some shamelessly nooby questions to ask. I have googled this stuff before and found plenty of information, but I'm still not sure. Any help or pointers are appreciated. Thanking all of you very much in anticipation.

1. What is the difference between NI VISA 14.x and NI VISA 5.4.x?
2. I have an instrument, I have a PC running Windows, what do I need to install other than the instrument drivers (VISA 14 or 5.4 or 488.2 etc.)?
3. What would you recommend for making the software (GUI), like Visual Basic or C++ or something, or this measurement studio thingy? Preferably something that doesn't cost me money.