1: Basically yes, simply picture in your head that bright white golden light is filling up your body and that your aura is completely clean, shines bright white gold and is filled with powerful light from the sun.
In the beginning it might be hard to feel the energy, but after doing it for a while you should start to feel some sort of warmth, or a tingling sensation or some other kind of sensation (everyone fels energy differently) while you draw in white golden light to clean your aura.
2: You can do it anywhere, but in public it is much harder to concentrate wince there are so many other people around which can distract you. If you aren't able to tune everything out around you at will then it is possible you will take in negative energy from other people by accident while trying to do this in public.
In the beginning only do it at home in the morning and evening, or do it outside in the sun in a quiet place, try to avoid doing it in busy places or places with a lot of people around.
Later on you will learn how to tune out everything around you, no matter how busy a place is, then you can perform this meditation anywhere at any time.
Right now I am able to enter a trance anywhere whenever I want, even in the middle of the city center during rush hour with little trouble. This needs to be practiced before you can do it and requires good control over your mind and thoughts. Void meditation is very important and is a good way to practice this.
3: You can say affirmations in your head, but I have noticed they have more power when you say them out loud. This might change when one advanced further, but at this point when I affirm things mentally they are a lot less effective and a lot weaker than when I say them out loud.
Your thought hold power, but your voice holds more power from what I can tell, because you are creating vibrations when you speak, which seem to produce a greater effect than simply thinking your thoughts.