Question 1: Difference between Live and Installed? Wow, huge difference. Is there a difference in going to work by walking and by car?..Not only that, updates, aditional installations (OpenOffice, google chrome, Compiz, etc), drivers for sound, video, wifi card in case you have issues with them.
Question 2: Yes you will loose all configurations and data collected unless you save them (data) in a USB stick.
Question 3: But off course you do have access to all software.