#3
absolutely.

just so you know, though, unless the harmony is dorian, you're not using dorian, just a minor scale with a raised 6th. there is a difference. don't understand it? that's fine -- as long as you understand you're not really using dorian, you're good for now.

as far as using the pentatonic and blues scales in the same solo, go to town. you're not limited to a particular scale.
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#4
Using a scale with several non-diatonic tones for a certain part of a solo is a good way to create tension (a.k.a. 'interest') in your soloing, which you can later resolve with the scale the harmony is based off of.
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#6
Yes. When a song is in a major or minor key you can use any note you wish.
And no, Guitar Hero will not help. Even on expert. Really.
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