4. can i change the tempo from 120 with my mouse or do i have to always use keyboard and type in 150

I don't really understand this one... When I start writing a piece I bring up the navigator with F2, and type in the BPM I want and I'm good. I don't see how being able to change the BPM with your mouse would make a difference. It takes less than 5 seconds to set the BPM as it is. Maybe you could be more detailed in your question, I may be missing something.

5. How can I change the Master volumes?

This can be done any number of ways. Starting with your speakers. Turn em down if they're too loud.

Hitting F3 brings up the main mixer and lets you adjust each individual channel's volume as well as the master volume for the entire track.

6. I keep the snap on if I want my music to be precise. Most people do. Sometimes I turn it off and adjust my samples a tiny bit for a more "human" sound.