Hi Lma,
1) When you move onto the next lesson is dependant on your comfort level with what you learned. I think if you can memorize what you learned in a lesson, then that should be okay. I also think it's acceptable to move onto the next section if even if you don't have it memorized. If you can play something out on the tabs for that lesson, that's also a good indication to move forward. With that being said, you should never feel "stuck" or like you have to stay on a section. The great thing about Guitar Tricks is our step-by-step learning system and also the ability to move forward or go back to an older lesson to review. Move forward when you feel comfortable and interested in the next thing. Remember, learning and playing guitar is supposed to be fun, so if you get kind of bored of a topic in a lesson, it's okay to move forward.
2) I think you should learn the songs you want to learn. We have a ton of songs in our library for you to learn and that is generally one of the best ways to learn some extra skills. For example, I learned a lot of new chords from playing old Beatles songs I really enjoyed listening to. Learning these songs also taught me how to switch chords quickly, too. I think it is perfectly acceptable to jump out of the lessons and go into a song tutorial.
Best,
Billy