Hi, this is Tony. 

I am currently helping Spiritual Works organization. My background is in meditation and Buddhism.  It depends what works for you. If you are starting out, I suggest 30 minutes at first and then meditate longer when you feel your concentration is progressing. For some people, it can be 1 hour or more, it just depends on the person.  There is no wrong or right answer. It depends what works for you.

You can use either. There is no definite answer. If you feel guided meditation can help you relax and meditate better, you should use it. The reason why there is more than one way of meditating is because some people prefer one over the other. It depends on the person.