#1
I have a USB compatible amp and I record using audacity. But when I listen to my own recordings, they don't sound mixed the right way. I've heard that percussion and vocals are usually panned to center, so where do i pan/mix the guitar?
#2
What genre of music are you recording?

Typically if it's very guitar-heavy music then it would do you well to double track the same part and pan one take hard left and the other hard right. This will give you a much fuller sound than if you were to record one take and have it going up the center. With lead parts, you *usually* hear those closer to the center.

I hope that helps.
#3
I'm going to respectfully disagree with you on this one. I would pan the guitars to about -/+ 48 rather than going all the way to full left and full right since this often produces a thinner guitar sound. Although I do agree with you on guitar solos being closer to center in the mix, and double tracking the guitar parts. Although sometimes if the mix calls for it or if you feel like tinkering around you can get some really interesting results by recording electrics three times per part (one being the most distorted you are using on the track, the second being a clean guitar track playing the same parts, and the third acting as a thickener track where you play the bass notes of the guitar track)
#4
It depends on the context and style. Like said about it is often hard left and right.

But it is also common to have a close mic panned one way and a room mic panned the other, given a sense of space.

Listen to these with headphones and you will get the idea.

https://www.youtube.com/watch?v=BwZ4Px57cWA

https://www.youtube.com/watch?v=hyWJCd1GYhw

Lead parts and solo's will often go more central like vocals.